I have nothing to add on whether it harms the bike or not, but I will say that having an inexpensive bike that lives on the trainer makes it a million times easier to both use the trainer AND ride outdoors. The trainer is always ready to hop onto and go, and my bike is always waiting in the garage ready to go. Not having the schlepping back and forth step makes it much more likely that I'll just get on the trainer or bike and GO. Works well for me.