Some feedback about why people might click on Ask a question without actually posting a question:
There's no better place to see which tags that exist on the site than to type something in the tag window of "Ask a question" and see what pops up. I do this all the time, when suggesting tags or participating in meta.
Other a alternatives is to start editing a post and click the tag window there, which isn't good if you actually have no intention of changing anything in it. Or to click add favourite tag, which has a worse GUI with no mouse-over with tag excerpt.
The general search feature of the site doesn't have a tag search, or at least I never found it.