Contrary to comments about not using reversers at lower speeds, US operators use reverse thrust in some cases to back the aircraft away from the gate without external assistance, in a procedure known as "powerback".
In Europe this seems unknown, and when you first see it done in the US you can't quite believe it. The power level seems very high for the slow rearward speed attained - slower than a tug might push at. Why is this acceptable in the US but not elsewhere ?