If you're uploading to #PeerTube, it's important to include tags, because these will make it a lot easier for people to notice your video.
PeerTube tags automatically appear as hashtags on Mastodon, so people searching or following those hashtags will see your video 👍
If you use more than one word in a tag, it will automatically be converted into a single phrase.
(PT tags have always worked as hashtags on Mastodon, but starting in Masto 4.2.0 the tags are actually visible below the video.)