Expensive regarding initial scan time, or repeated scanning?
This particular user has a habit of saving PSD files all over her profile instead of in an organized structure, and since I don’t want to pick up 50GB of data, including all of the other file types in her profile, this seems to be the only way to do it.
As soon as there is a “!”, everything is scanned, and there are no optimisations, even for anchored unignores.
This will mostly be ok, as filesystem watches should help out, but I suspect there is a lot of cruft in the home directory in general which will repeatedly trigger filesystem watches.