One of the things I have started to appreciate with Drawbars is the need to use a foot switch. When first playing with them, I used to set a Drawbar combination and just play with that setting. Part of the beauty of using the Drawbar sounds though is the electronic Leslie cabinet, which is pretty accurate when compared to the originals. This effect is achieved by the DSP settings and the continual use of switching backwards and forwards from fast to slow. This is where the foot switch is often useful. Its use will be dictated by your own needs and again as with so many things musical, there are no rights and wrongs with this. Try playing a song (any song, it doesn't matter which) in such a way as the Leslie effect doesn't get time to settle on fast or slow. Its almost as if you are trying to keep the effect permanently winding up or down. With a little practice you will start to become attuned to the effect and will be able to use it more judiciously on held notes, almost in the same way that some singers add a vibrato effect halfway through a note.