Last year I had to remove a large number of slotted screws from a ceiling. The only sensible way to go about it was with a cordless driver, but it was a messy business. To make things worse, the heads were very hard (and brittle) so I had quite a few broken screws which had to be removed with pliers. Maybe a screwfinder would have come in handy for this job, if I'd known they existed.
I would still use slotted screws where they're going to be on display when the job's finished, installed with a screwdriver of course, and driven home so that the slots are aligned.
I also like to use slotted screws in a location where they're liable to get very dirty, or clogged with paint, and I might need to remove them later, for the reasons Noseall gives.