Multi Angle Valve Seat Job

Ok, I have a 20valve silver top, with Black top throttles and black top computer, TRD head gasket, Black top extractor. Very soon I want to take off the head to get it port and polished.

Lately I have been hearing about getting "valve seat job" done, read somewhere that its a great improvement for most 4age especially the 20valves. Can someone explain what this is? and if I got a 3 or 5 angle job, what would be the best or right degrees of the angles needed? I asked a machine shop owner here about it, he said He can do it for me, once I know what angles I want.... this is...IDK what angles I want ...so one of you smart GURU's here can plz help me?