I and my fellow crew members will always call vacated, and where, whether its asked for or not.
If I'm on to scare birds I will add a positive "wildlife dispersed" to confirm the runway is safe. If its for a runway check I'll add "nothing to report" or "<X> reports when you are ready to copy" to indicate that there are either no problems or X number of problems (normally AGL fittings whose bulbs have gone)
At night I also have to ask for my onwards clearance and during the day it gives ATC an idea on roughly where I am as we are on own lookout.
There's also the added benefit that the Operations Co-ordinator monitors the air frequencies and will insert my inspections into the log when he hears me vacate.
Essentially its primarily a safety thing, to positively confirm that I am clear of the active runway and complete, secondary to that is the 'bolt on' report that the runway is confirmed as safe for use.