Every question requires one of the tags [feature-request], [bug], [support], or [discussion]. Why is this so?
The 'obvious' answer is the idea to structure the various meta sites in a standardized way. What is likely not obvious is that this is actually used beyond what what can be done with usual tags.
For example, a question tagged as "discussion" might show up as Hot Meta Post on main, a "bug" question will not but instead it will by brought to the attention from SE staff.