Reversing isn't allowed at some clubs/meetings, others allow it.
Our local club allows reversing, and I wouldn't consider running forward only.
Some of the racers at are club are fairly new to RC, and crash a lot. Without reverse, the marshals would be very busy! Even the top guys make the odd mistake, and reverse means they can back off the barrier without the help of a marshal - quicker and safer, as long as the stuck driver doesn't reverse into the path of another car.
Why not get a speedo with reverse lockout? Best of both worlds. Reverse for bashing/practice/local meetings, forward-only for when the rules dictate it.
My LRP speedos have reverse, but can be converted to forward-only with the press of a button.