Breaking the 4th wall - directly or indirectly

Question...... when is it appropriate to break the fourth wall? I appreciate that it is a broad question and some plays specifically require you to break down the fourth wall but I'm curious, is it acceptable for a director to ask his/her actors to break the fourth wall in a standard play that does not call for it (by breaking the fourth wall - I dont mean completely breaking it and sitting down and talking to the audience one on one....... more so with reference as using the fourth wall to deliver monologues as if out a large window and having an actor stare direct at the audience as if looking through them - and in so doing save set construction and large bay windows and lighting issues etc etc etc etc etc) what does the community think?