Worth mentioning is that converting the heading you are flying to maintain a procedural track to a radar vector
may allow me to take you lower than I can if you stay on the procedure.
Example:
on this procedure, the MEAs on the legs inbound to the localizer are 5000 and 7000 feet - yet my MVAs I can use on vectors are as low as 3,000.
I want to get aircraft down for a visual or for the ILS approach, so I'll say to aircraft checking in "fly present heading (taking them off the procedure and negating the requirement to honor the MEA), descend and maintain 3,000 (the MVA).
It's a bit of a paper chase, but one reason it's done.