i dont do this, but i think a good reason is if someone searchign a forum for a certain topic and dosent find exactly it or finds something but they need more info on it then they could post in that topic and ask a similar question like if someone asks about a UTH in a wood enclosure and they cant find it anywhere but they find a thread from 3 years agho about putting one in a plastic enclosure, they may decide instead of making a new thread just to post a reply in that one and ask. but im not entirely sure. //
on the otherhand people who research 1+year old topics and jus tsay haha or lol or thats funny or somethign of the sort. thats kind of pointless imo. but to each their own.