Tags are used in multiple areas of Wednesday including Content, Contributors, and Pages. Tags are a powerful way to group videos by a particular data point (ie Location, Department, etc)
Things to consider when using tags:
Standardize your tags
Come up with a unified set of tags to use internally
If you have two tags that differ even in capitalization it will not group the videos together. Use the autocomplete feature used for other tags as a way to identify tags already in your account.
Keep your list small
If everything has a unique tag, then tags are not helping you narrow down your data set.