Rolf Silber
Veteran
this was one of the biggest signs of a poor director, if he's unable to give direction without "showing" the actor what to do by acting it out himself for them.
If this would be true, Federico Fellini would have been a poor director. But, yes, usually one should not do it and mainly because it can "fence in" creative impulses coming from the actors and, strangely, from the director himself as most "acting out"-directors don't realize how terrible their acting is and - worse - that they may over-look something interesting coming from an actor. As a director needs to balance his own concept of how things should work in an ideal universe, where everything works like he wants (definitely not ours) with this other impulses coming in, he better should seek for good analogies and metaphors to convey what he wants and at the same time give creative impulses the appropriate leeway.
The great Italian theater director and playwright Dario Fo is not imaginable without acting things out himself - but, coming from "commedia dell'arte", his acting out was "inclusive", one step in of getting to how a scene may work - the director co-rehearsing, in a way. So one may "act out" things at times but only if one has the ability to do it, when it is asked for and when it is a process not ending in puppeteering actors. At times so, with extras.... different story.
In the end all this questions will get reduced to one: "What kind of a director do you want to be?"