apart from the obvious when it is actually raining; when is it suitable to use them? standing water only or are they of use on a damp track with no dry line?
I wouldn't run full wets on a damp track. As it dries throughout the sessions they'll just shred and fall to pieces. Never owned full wets myself but I've seen it happen to others.
DD I think you will find that unless the track is realy wet with lots of standing water to help cool the tyres, what desmondo says holds true. Full wets are for the true TD fanatics
Try to keep the full wets for when there is standing water, for damp tracks its handy to have a set of worn wets that you dont mind trashing, can usually pick them up quite cheap from some of the club racing paddocks