There's another issue that hasn't been pointed out yet.

Brushless motors can run equally well in either direction.

However, some DC brushed motors often can NOT. There is usually a built-in timing adavance in the way the magnets and brushes and so on are built that makes the motor run better in one direction than the other.

Sure, the motor will run backwards, but it won't produce as much power and will draw more current in the process. It does vary a lot with the motor, and there ARE brushed motors timed for equal running in both directions. So, if you want to run a DC motor backwards from the designed direction, you should do a bit of research or comparitive testing on the bench to make sure the motor wants to do backwards well.