YouTube comments live as long as the video does
A YouTube video can keep getting views for months or years, and its comment section keeps getting read. A useful comment, a timestamp to the key moment, a clarification, a question others share, can collect likes long after you posted it.
Creators pin the comments that help their viewers and heart the ones they appreciate. Both happen to comments that add something, which is what the "add something useful" goal is for.
When you describe the video in the box, include a moment or two with timestamps. The drafts can then point at them.
Leaving comments as a creator
If you run a channel yourself, comments on videos in your niche put your channel name in front of viewers who already watch your kind of content. The rule is the same as everywhere: talk about their video, not yours. No links, no "check out my channel".
On your own videos, you can pin a comment of your own. Use it for a correction, the links you mentioned, or a question that invites viewers to answer, and reply to the early comments: a busy comment section is a reason for the next viewer to stay.