Bill, you said, "However, it may make subsequent editing a little more difficult" There you have it!!! If a person doesn't need to use Step Record, you can do this. Trying to correct a measure, you would be half in one and half in another. Also, there may be an automatic trigger if one uses an Intro for the rhythm to respond correctly to not be out of sync. I have done about four songs starting with ad lib. What I felt I had to do was do a few tries to find out where my ad lib would stop. I would find that I would have to start playing perhaps on the second or third beat for it to come out correctly when I wanted to start the rhythm.

You bring up a good point by stating that there may be another way. I thought that doing an ad lib, I could go later into Step Record, bring up the Control track and press the Stop/Start button in the right spot, which shows Rhythm Start. It doesn't work. I even tried going into the Rhythm track and found that was no help.