Why do I have to assign tags to drop-down ticket fields?

Question

When creating a drop-down field, I noticed that I have to assign a tag to each choice. Why do I have to do this? How does this work?

When you assign a tag to a drop-down ticket field choice, the following will occur:

Any time you apply a tag to a ticket, the corresponding field choice is selected.
Every time you select the specific ticket field selection, the corresponding tag is applied to the ticket.

For more information on how tags and fields relate, see this article: Understanding tags and ticket fields.