Cutting up fresh fruit might be desirable if you’re travelling with a small child (you should even cut grapes in half) and small knives are also permitted.
But I don’t think that’s what they’re getting at. If you’re travelling without hold luggage, “on the go” means for your entire trip, not just while on the flight/in transit. And you may well want to have the ability to make a simple meal in a hotel room rather than eat out.
“Prep food on the go” means exactly what you think it does: preparing your own food in the airport or on the plane. How often anyone actually does it (especially w.r.t. things like a coffee grinder) is anyone’s guess. But the regulation is spelling out the letter of the law: blades less than 6 cm are permitted.
Since the page you linked specifically mentions certain things like smoothies are not permitted, it may be possible to make your own (by bringing fresh fruit and a hand blender). Particularly if you are traveling long distances with a child or infant (or have specific dietary needs), I can see where that would be helpful.
It does conjure up some interesting images, though. (e.g., “Iron Chef Seat 33F”)
Credit:stackoverflow.com‘