We normally frown on large scale _cosmetic_ changes, mostly because it breaks git's history (very useful) and makes merging branches harder and more error prone (very annoying).
However we require, right now, such changes to remove our old, mcs-based, pre-processor (pmcs) so it's a _good_ time to address the old, unneeded availability attributes - since most of them are re-written for our next milestone.
This won't change the final application size in most cases, as the linker removes them, but it will make the (unlinked) platform assemblies smaller. This means they will load faster (e.g. by mtouch, mmp, IDE, workbooks...) and will reduce the time/memory needed to reflect them.
Vincent Dondain
Sebastien Pouliot