Tags are an important factor in YouTube SEO, though not as important as your title and description. Tags help viewers find your content in the search results and they help the YouTube algorithm understand your content. This is especially important in the early stages of your channel when you don't have a large following and YouTube's algorithm isn't familiar with your content.
By adding relevant, long-tail tags to your videos, you'll make it easier for YouTube to understand what your content is about. By doing so, it's more likely the algorithm will showcase your videos in the search results and the suggested videos column, increasing your views and audience.