Crabbing is still coordinated flight, you're just correcting for wind drift. A side slip is what you would use on a crosswind landing, the nose of the plane is lined up with the direction of flight, but you have one wing low and stop the turn with opposite rudder. A forward slip is what you would use to lose altitude on a turn from base to final, the nose of the plane is not in line with the direction of flight.
Another problem with slipping Cessna's is the fuel problem. You force the fuel in the tank away from the fuel line. I've experienced this first hand with an engine failure. I tried it again later at altitude and sure enough, hold it in a slip for long enough with one tank selected and look at your fuel gauge indicate zero and your engine will soon quit.