It depends how it’s set up.

A subreddit is basically a sub forum, and having a ton of subforums can create clutter real quick. But a single thread is often too cluttered with too much going on to keep track of depending on the topic.

Example, say you have a games forum with a thread about Skyrim. That’s gonna be pretty useless because it’s going to move super fast and be hard to keep track of anything. A subforum/subreddit would be better in that scenario so you can have multiple threads about one topic.

But a thread about say monitors is fine, the discussion moves slower.