There is always a "Gray Area" / And for every Industry Standard there are 100 caveats
If you are going to “Break a Rule”...
My advice is to make it count and the project should be worth it! / This is a major rule that should almost never be broken. / Most people do not have the skill to film a scene environmentally would look good enough to make an impact and not hurt a performance. / Using another Actor on screen with the auditioning Actor is very frowned upon. It can hurt a performance if the other Actor is bad or not the appropriate type for role. / Even an arm or hand from an off-screen reader can be distracting and look Amateurish. / BUT... / On occasion it has been a worthy gamble. / A challenging scene with a lot of Action can come to life when taken out if the confinements of a Self Tape Frame.
Running from a bad guy.
Having a Physical Altercation.
A better performance may need some reality infused to really showcase the right emotions or reactions. / Self Tapes do not need music or sound effects to be effective. Casting is looking at the Actor’s performance. / But there are times when an Actor can get into mood by hearing some underscore or music that would be played in the environment of the scene.
In fact, a great coaching technique I use is listening to a dramatic score that is typical of the genre to find the right tone of the performance.