What are the benefits of practicing Sila?

First of all, keeping precepts will help lead one to a good rebirth because it is good karma. Secondly, having good sila is necessary to provide a basis for success in meditation.

Sila provides protection (from bad outcomes and consequences) according to the Atta-rakkhita Sutta.

Those who engage in bodily misconduct, verbal misconduct, & mental misconduct leave themselves unprotected. Even though a squadron of elephant troops might protect them, a squadron of cavalry troops, a squadron of chariot troops, a squadron of infantry troops might protect them, still they leave themselves unprotected. Why is that? Because that's an external protection, not an internal one. Therefore they leave themselves unprotected. But those who engage in good bodily conduct, good verbal conduct, & good mental conduct have themselves protected. Even though neither a squadron of elephant troops, a squadron of cavalry troops, a squadron of chariot troops, nor a squadron of infantry troops might protect them, still they have themselves protected. Why is that? Because that's an internal protection, not an external one. Therefore they have themselves protected.

Your entire relationship with the world changes. Interpersonal activities turn out more positively as they approached with discretion and honesty. As you meet success in your relationships, your overall demeanor improves. You grow happier and your quality of life is enhanced. Furthermore, reflecting on your actions makes it much more difficult to engage in activities that you may regret later. Sila also builds on itself. The more you discipline body, speech, and mind, the easier these actions become to maintain and engage in. As you grow in practice, the benefits become more obvious and pervasive. Mindfulness improves and concentration is more stable.

And if you want some more mundane benefits - you'll probably lose weight, sleep better, and more often find yourself in beneficial circumstances. People tend to like nice people. :-)

To offer a more personal answer -- about 6 and a half years ago I decided to begin keeping the 5 lay precepts scrupulously, as an experiment. Not that I was in the habit of, say, killing, lying or getting drunk prior to that. But my temperamental tendency was to be flexible and not want to make others uncomfortable socially. Specifically, I adopted a strict vegan diet, gave up alcohol altogether, and began being more careful about speaking truthfully and not taking anything not freely and obviously given.

The results? The words stability and clarity come to mind. I am less wishy-washy, a sense of integrity supports my practice. And there is more of a sense of self-respect now. I know I can be trusted and I think others sense this, as well. Try exploring the precepts both in their explicit and implicit meanings and try keeping them scrupulously for a few weeks. You will see the benefits for yourself.

Just like a house needs a strong foundation to last a long time, one would need sila as the foundation upon which the entire Path is built:

"Thus in this way, Ananda, skillful virtues have freedom from remorse as their purpose, freedom from remorse as their reward. Freedom from remorse has joy as its purpose, joy as its reward. Joy has rapture as its purpose, rapture as its reward. Rapture has serenity as its purpose, serenity as its reward. Serenity has pleasure as its purpose, pleasure as its reward. Pleasure has concentration as its purpose, concentration as its reward. Concentration has knowledge & vision of things as they actually are as its purpose, knowledge & vision of things as they actually are as its reward. Knowledge & vision of things as they actually are has disenchantment as its purpose, disenchantment as its reward. Disenchantment has dispassion as its purpose, dispassion as its reward. Dispassion has knowledge & vision of release as its purpose, knowledge & vision of release as its reward.

"In this way, Ananda, skillful virtues lead step-by-step to the consummation of arahantship." ~~ AN 11.1 ~~

The benefits of morality are many.

According to the Buddha, the main purpose of morality is non-remorse (AN 11).

Or, there are five benefits, including attainment/guarding of wealth:

“Householder, there are these five benefits for the virtuous in the perfecting of virtue. What five?

1. Here, householder, one who is virtuous, possessed of virtue, obtains a large fortune as a consequence of diligence; this is the first benefit for the virtuous in the perfecting of virtue.

2. Again, of one who is virtuous, possessed of virtue, a fair name is spread abroad; this is the second benefit for the virtuous in the perfecting of virtue.

3. Again, whenever one who is virtuous, possessed of virtue, enters an assembly, whether of khattiyas (warrior- nobles) or brahmans or householders or ascetics, he does so without fear or hesitation; this is the third benefit for the virtuous in the perfecting of virtue.

4. Again, one who is virtuous, possessed of virtue, dies unconfused; this is the fourth benefit for the virtuous in the perfecting of virtue.

5. Again, one who is virtuous, possessed of virtue, on the breakup of the body, after death, reappears in a happy destiny, in the heavenly world; this is the fifth benefit for the virtuous in the perfecting of virtue”

-- DN 16 (Nyanamoli, trans)

The Milindapanha also gives a nice description of the virtue of a moral individual:

"A moral individual, great king,

1. is like an antidote in destroying the poison of defilements;

2. is like a medicine in curing the sickness of defilements;

3. is like water in taking away the dirt and mud of defilements;

4. is like the jewel treasure (a gem said to grant wishes) in bestowing all attainments;

5. is like a ship in helping beings go to the far shore of the four floods;

6. is like a caravan-leader in helping beings cross over the wilderness of birth;

7. is like wind in extinguishing the threefold fire and heat;

8. is like a great cloud in replenishing the mind (as with rain);

9. is like a teacher in causing beings to train in wholesomeness;

10. is like a good preacher in causing beings to see the path to security.

Morality is considered to be the foundation of the holy life, along with right view (SN 47.3).

As Buddhaghosa says,

Dare anyone a limit place
On benefits that virtue brings,
Without which virtue clansmen find
No footing in the dispensation?

-- Vism I.24 (Nyanamoli, trans)

As for needing incentive, sometimes it is important to distinguish between moral precepts and actual morality. Keeping the precepts is important, as it serves as a general frame of reference in corralling the mind, like fence posts. It is not enough, though, and the mind will still tend to rebel against the precepts if one does not build a fence of true morality, which entails mindfulness. Through mindfulness, true morality is attained at every moment.

“The currents in the world that flow, Ajita,”
said the Blessed One,
“Are stemmed by means of mindfulness;
Restraint of currents I proclaim,
By understanding they are dammed”

-- Sn 1035 (Nyanamoli, trans)