I don't know about what this forum is like but with massive member lists of inactive members it can tend to make the forums run slow.

I am for a cleaning but three months is a little short of a time. I would think that two years of inactivity will usually mean that they are not comming back.

Some other good things that come out of cleaning is an easier searchings of the member listings. I would much rather be running through 1000 names than 12,000 names most of which are inactive.