Hi Ron, welcome.
Whether bikes are useful depends on a) what vehicle you arrive in, and b) what you want to see:-
Vehicle - If your'e in a car with tent, you can use the car to get about for food & drink supplies. A motorhome is best left on site (otherwise your pitch will be gone when you return !

, and a bike is good to visit the supermarket for breakfast etc.
Seeing things : The quickest way to see Arnage, Mulsanne corner etc at night (essential !!) is by bike, as the traffic jams are legendary, and the Gendames are quite likely to breathalyse car drivers (with good reason

So if you can, do !!