I use to do that... when I was a kid/teenager but not since. I will do it for 2 seconds to position myself but that's it.
If you are concerned about cheating/using your back/arching then you are using to much weight period....
It's the same with curls. If you can not do it seated or your back against a wall it's to heavy.
it's about form, not cheating or your muscles are not getting the desired work.
Do you bounce off your chest if it's legal? I use to do that as a kid also; sometimes. Now I do a 2 count at my chest. I dont rest it on my chest but it is touching.
Try it this way. Forget about HOW MUCH you can do. Drop 40 lbs. Do each rep SLOW. Touch your chest and say 1 thousand one. 1 thousand two, then press it up. at the top Push your chest UP without raising your back. Do a 10 set of those and I bet your chest is burning like it never has.
You should feel your bench workout in your chest, not your arms. Yes it's fun to max out but find your right weight and it will hit your chest a LOT better. Feel the burn literally in your chest on each set.