I wondered this.... If there was a forwarding system we could give people comments we received that applies to them... also we can more easily send spam and proof of stuff to mods/admins.
The downside to flagging is all the staff get to go over it; though those reports can then be tagged "fixed" or "dealt with" or so. The upside is it's one clear forum/section of reports they have to go over, they don't need to go looking for it.
The downside to leaving a report on their profile pages is they then have to read all that, probably feel compelled to write a response, etc.
Which they prefer I don't know; over to them. I know forums where there's a small caption box to go with the flagging, to leave a short reason why. Or perhaps a drop-down box with a choice of a few options. (Spam/misplaced/non-English post/flame alert/iffy first post, what have you.)
Not sure about the flagging in the forums, I always check to see which mod is on at the time and post link directly to spam. However comments under games i flag. Other wise the mods page might get spammed up. Plus the forums are more active than some game comments so more direct action is needed.
