To add on this adds is not only important, relevant tags is very important especially for channels just starting out...My channel is were it is now thanks to the optimization of my videos with relevant tags.In my experience tags help videos relate to each other. if i upload two videos with the same tags they usually come up at the side as related. The way you should look at it is Youtube uses title description and tags to figure out what your video is but ye i do think tags are used in the initial stage. Once youtube figures out your video it focuses more on metrics, e.g. engagement and watch time.
This and i would like to add that you can make your videos rank higher by linking the tags,video title and description together. By using this technique your video is going to be ranking higher than videos which have higher views than your video for some time.tags does help a little. personally i use tags a lot in all of my videos, it helps me know where i rank when a specific content is searched, well with the help of tube-buddy of-course. its quite important especially for small youtuber trying to grow their channel.