Even when Forums were the de facto way of interacting online, I never understood the problem with Necroposting. It just seems natural that in a medium where no conversation is exactly "real time" it is actually a good thing (and shows the vitality of the forum) that old conversations can be revitalized and spring up from the depths of the archives. Otherwise, I always felt you got tens of threads all about the same theme, where one big centralized thread seems much easier to parse and readthrough.
The funniest thing about necroposting is when people on Reddit bring it up as a bad practice, when reddit is "new-comment" agnostic.
Also, I always found it special when an old thread of mine got a response months or years later. Like a little drive-by interaction on the ether.