Reply or subscribe

When wanting to add one's twopenw'th to a thread should you use "reply topic" or "subscribe", and why?

just click reply to make a comment on that topic. If you subscribe you'll just get notifications anytime that user posts something. At least that's my understanding of how it works.

As above.

Reply = post your reply.

Subscribe = you get notifications when someone's added to the post.

Handy if you need advice urgently.