Alot of the time its there procedure for when they can hand you over to tower for a radar controller.
And for a procedural controller they use it for knowing where you are. ie they can then decend another one in the hold or possibly send the next one outbound on the procedure if certain wx limits are good.
Or it might be the point that birdy gets told to shift it off the runway and then at 4 miles report you will get your landing clearance.
Also different units have different policy and also different controllers at the same unit some will ask you and some won't.
The only real issue for pilots is that you can't decend with the glide until you are established if so cleared.