First: Respect to Keith for pulling through with fixing those warnings!
Second: That may reduce the memory footprint of the X server but aside from that, at least for the end user, it won't do much.
Third: May god (if there is one) have mercy on the poor soul that'll commit the first thing that introduces a warning into the new codebase...because Keith won't have any. (at least I wouldn't after fixing over 1000 warnings)
I think warnings can also indicate potentially unsafe behavior that is not guaranteed to cause a bug but might under some circumstances.