There's a sticky "I am stuck!" thread so if you're stuck in Aquaria you go there, sticky threads can be bumped whenever, it's partly why they're stickied.
If you see a thread with awesome content that's over a few months old you don't just go in there and post "Omgawd that's awesome!" or anything like that, it adds nothing to the thread, it's simply a bump then.
If you see an old topic that interests you and you have content to add I'd say go right ahead, however if there's a thread with a question that's 2 months old you can't expect the person who asked it to still be around, is useless.
That's how I look at all of that anyway.