What are the benefits and setbacks of grouting a frame in masonry construction?

If grouting is done properly it will not cause any issues with the frame. It will actually improve the sound deadening qualities. Unfortunately, thin pumpable slurry is often used and the excess water in it causes rust. Grout should always be hand troweled, never pumped.

For fire rated openings, you should verify with the frame manufacturer that if a bituminous coating is used to protect the steel frame against any corrosive effects of the grout its use will not negate the fire protection rating.