Most flight is done while crabbing. Unless your heading exactly into the wind or away from it, you are crabbing if you are flying from point A to point B. Full size pilots pull out their E6B to determine how many degrees off their intended ground track they must fly at to reach their destination - well that was the way it worked when everything was done with dead reckening. Later radio aids and now GPS remove much of the calculations and the work load.

So now about the only time people are greatly aware of crab angles is when they are looking at roads or runways. Yes, you can crab all the way down to contact with the runway, it doesn't matter if it is full size or model. But unless you are flying a B-52 there are these things call landing gear that would prefer to be aligned with runway when they touch. So what to do?

Stay in the crab, then straighten out with rudder at the last moment. Works fine

Slide slip to compensate for the cross wind, touch down on one wheel then slow down to align on all three. Also works fine. But you generally crab until you go into the side slip.

Now for example if the wind is from the right side of the runway, a side slip uses right aileron and left rudder. If you are crabbing, the ailerons are neutral and you kick in rudder at the end to align with the runway, but you also add aileron into the wind to hold the windtip down as you slow down.

Finally, a forward slip with the wind from the right side of the runway, you use right rudder and left aileron. In a full size airplane this puts the runway between the nose of the airplane and the wingtip. This gives the pilot a really great view in two seat airplanes with side by side seating, and is really great fun. It is also draggy as all hell since you use most of the rudder to shove the side of the airplane into the airstream. But at the bottom of the barrel, you must align the fuselage with the runway and drop the other wing into the air to land.

If you are more advanced with your model flying, I highly recommend you take your side slip to the extreme and try a knife edge approach to landing. Instead of gentle bleeding off altitude and speed, make your approach to the runway at 50 to 100 feet of altitude. When you reach a point that is 30 to 60 degrees up from the end of the runway, toss the airplane into knife edge and you will just drop out of the sky without picking up speed. Then as low as you dare, roll out and flair. Works best with models with big round cowls (drag buckets, but those Russian acro airplanes with radial engines make great models), but most sport models can do it.