Yeah, it takes the stretch reflex out of the lift.
Years ago Brooks Kubik wrote and article on pressing from the pins in his rack and worked up to a drug free #405+.
I think he may have also worked down to the bottom pins, slowly increasing the ROM.
I think at most, it would increase your strength off the chest or at the start of the move, and as Herd said, if you are gonna compete, that is probably a pretty big factor.
As far as safer!? I cannot tell you yes or no, since a dead start at the bottom without staying loaded, does put a lot of strain on the cuff muscles.