Adding metadata (custom fields) for taxonomy terms is important since it allows us to add more data to term objects. These data allow us to add a more visual description to the term objects beyond the default description which can help us design in the front end.
There is a lot of info that can be useful for terms. This is just an extremely small sampling of ideas:
Term featured image.
Custom color for each category to differentiate them in a magazine website.
Storing the meta title, meta description via an SEO plugin.
Category templates that can be re-used (like page templates).
Attach an icon to a term.
Theme sidebar position.
Privatize posts that are in a specific category in a membership plugin.
MB Term Meta simplifies the process of adding custom fields to terms by using the same syntax in Meta Box for posts. No more learning curve when using this extension.
Besides, it supports all the features from Meta Box such as all field types, cloning and validation.
Uses native term meta API
Uses the same syntax as Meta Box
Uses the same UI from WordPress