Upvote:1
It’s a good idea to make sure you don’t miss your flight.
Some airlines will cancel your booking though, for example United airlines as stated in United’s Contact of Carriage have the right to cancel your ticket:
The types of improper reservations that UA will cancel without notice include, but are not limited to … reservations made for the same passenger on flights travelling on or about the same date between one or more of the same or nearby origin or destination cities; and reservations with connections that depart before the arrival on the inbound flight.
Therefore, if you do book two flights I recommend doing it with different airlines when it shouldn’t be a problem. A lot of people cancel flights these days and it isn’t unusual.
On the other hand, though, flight tickets are sold together on the basis that the airline thinks you can make the connection. Therefore, if you miss the connection it will be the airline's fault.