I can't find the cite so my memory may be faulty. . .

I believe that if I ingest at least my basal metabolic rate worth of calories I am unlikely to lose muscle when dieting. I recall a study comparing dieters that were and were not exercising and also comparing the type of exercise, aerobic or aerobic plus resistance training. All lost fat not muscle. But the reason likely was that the diet did not severely restrict calories.

But I agree with you folks, mixing it up on the exercise front is good. For motivation and for health.