We have these safety benches at all three of my clubs. Two of my clubs have at least 8-12 benches, and we typically claim a bench and keep our stuff on them & around them. If more guys come and we are out of benches, then we share benches, or the new guys start them on the ground. That's just how we do it at those clubs, since we rarely have more pilots than benches. One club even has a safety bench just for engine break-in, it's placed far away from the flight line and pavilion so the noise and exhaust won't bother anyone else!

I've also been to another club with only a few safety benches, and since they frequently have more pilots than benches, their policy is to just start your plane on the bench and then clear it for someone else.