I'd say the following will occure:
1. 3 way end up leaking.
2. more kick.
3. potential to break pump arm
4. wastful on air.
6. more potential to bounce (and for some I guess that could be a plus...)
7. wear out ram faster
~ owner & driver of cars ~
i guess if you left it there for a long time, it could mess with the threads where the pump arm attaches to the back block, but beyond that, there shouldn't be much of a problem.
That should never happen if the block is spaced like it should be. Thats the only reason that happens is due to block smack. Pressure only would effect the time it takes for the threads to weaken to the point of failure.
"An elegant weapon; From a more civilized age."