Run Over the Ground Crew
At my old carrier, we never moved anything until we got the 'all clear' signal. However, that SOP was not always the procedure. A couple of times over the years, the crew, in an effort to be fast (which, to inexperienced crews, "fast" means better and more competent) ran over the ground crew.
So, to preclude injury (to the ground crew...and to the captain when the engineer implanted a spanner into the captain's head), the procedure was established that nothing...absolutely nothing...was done until the 'all clear' signal was received. After that, the after-start flow was commenced and the taxi clearance was requested.
It's difficult to slow these younger guys down a bit. You're saving, literally, only seconds by taking the chance of hurting someone and/or damaging equipment.
Is it worth it?
Tom