Do YouTube Tags Still Matter?
Tags used to be one of YouTube's most valuable SEO tools - stuff enough keywords into them and one would find a clip for every search query. This changed drastically, with the new YouTube algorithm valuing titles and descriptions more than tags. However, do tags still matter at all, and how should we use them?
What Tags Can and Cannot Do
Tags give YouTube slight context clues about what a video is about, and can help differentiate between similar search queries. This is useful in case of homonyms (e.g., differentiating between orange the fruit and orange the color), and slightly misspelled search queries. However, tags' impact on the ranking is minimal. There are some things tags cannot do, however - they cannot compensate a clickbait title, a boring description or a boring video that fails to grab the viewer's attention. Stuffing irrelevant keywords, hoping that YouTube will fail to understand the video and list it under a search query that has nothing to do with the clip's theme will most likely not work, and might get the video penalized. Prioritizing tags over title and description is a bad idea. If one spends hours upon hours optimizing the video's tag list while neglecting the title and description, the former has very little impact on the video's fortunes.
Practical Tag Optimization
When optimizing tags, focus on a short list (preferably 10) of thematically similar tags. Include several variants of the same keyword (e.g., misspellings), and make sure to include the channel name if one wants the video to appear in one's catalog. Do not overload the list with unrelated longtail keywords, as this will baffle YouTube's algorithm and may damage the video's ranking.
What to Focus On: A Priority List
When optimizing a video, one should focus on the following in order of priority: An informative and straight title; a description that provides some context and information about the video; proper closed captions (which also help the algorithm) and tags. This roughly approximates the worth of each element - the title is the most important, tags are a distant fourth.
Conclusion
Tags are a small part of a video's SEO, and are primarily useful as differentiators between similar search queries. However, they cannot make up for a video's lacking title, description or content. Remember that tags are only a minuscule part of SEO optimization, and focus on more important elements of a video's listing.