Auhhhhh the slip
Depending on the airplane......The airspeed does not have to be increased.
Procedure would be to yaw the airplane with rudder, and opp aileron.....ex: right rudder, left aileron. In this case one is looking out the side to keep alignment with the runway.....airspeed is not a real factor if entered a few knots above approach speed.
The buff would "stray" many degrees and the landing gear was aligned with the runway......prior to touchdown we used rudder to align the a/c...(thank the big guy for AILS) .In Thiland , I once witnessed we were 20 degrees from the runway heading. (out of the envelope)
The buff was slow to coorporate with the input.......it was like too much negative expo.....Point: Rudder is a tool we need......it just depends on what we are flying.
Sub note: We always had to input aileron to complement the rudder.....
I hope I made sense of this difficult topic.
Doc