I would love to have an option to exclude tags that belong to ONLY checked items from being autocompleted in the search field. So if the option is enabled, a tag that doesn’t appear in any items that are unchecked will not be included in the autocomplete list in the search box.
Example: I’m working for a client named Bob. So I create a tag @Bob so I can use it for any items I I have to discuss with Bob every time I see him. At some point I finish the project and all my @Bob items have been checked off. But now, for years to come, every time I go to search for other tags “@Bob” will appear in the list, even though it’s unlikely I’ll ever use that tag again. Multiply that by all the other clients, contexts, etc that will become outdated but will keep popping up in the autocomplete list every time I press @ or # and it won’t be long before you get a really long “autocomplete” list where many of the items are irrelevant.
Of course, it’s useful to have the option to have every single tag I’ve ever used appear in the autocomplete list in case I’m ever doing a search that needs to include all completed projects, checked items, etc. But in my opinion it should be just that, an option, much like there’s one for checked items to appear in searches or not.