Tags help people find your content who are interested in the subject your content covers. For example, some people like learning about cryptocurrency while some others prefer only to read about ethereum. By having both the tags "ethereum" and "cryptocurrency" in a post about Vitalik Buterin all the people interested in general cryptocurrency and specifically ethereum can more easily find your content with the tags. If the content is good they will probably upvote the content.
More important is using the tags honestly. Misleading people with tags such as using the "introduceyourself" tag in all your content will justifiably get a lot of flags on your content.