In the case of torrents, I think it would help people see what's new and what's not. Though it only takes a click to see the date of the post. I don't know if it's worth the effort? (completely oblivious when it comes to coding and such)
He's talking about before you have to click it, e.g. in a sub-forum, browsing the list of torrent threads.
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I agree, right now the only way I check what's new and what's isn't is by looking at the number of thread views. Less views = more likely new. But that's sketchy and I'm afraid I'd might miss something and I always re-visit threads I needn't re-check accidentally... but that's how I have to go through threads.
Some easily noticeable way to absolutely indentify if the thread is new without having to click the thread itself would reduce unnecessary traffic...
The best two ways are either:
putting the original thread post date viewable in the subforum(like mentioned by jezbzz)
or
putting an option in user preferences to either view sub forums by thread start date, or view forums by latest reply date. So both Nazis and Socialists can get what they want.