.... for example...

Look at this movie of a Camel landing:

http://www.rcuniverse.com/forum/m_18...tm.htm#1844994

The plane decends with the fuselage a bit sideways and one wing dropped. That is a slip. It requires rudder input. The pilot does it to increase drag on the plane so that it decends faster without picking up airspeed (as would result if one simply dove). You can do the same with your model for kicks. If you were landing dead stick and found yourself high on final, you could do the same thing to avoid landing long.