In the United States, adding "already" with a blunt command implies that the speaker is becoming impatient or believes the person to whom he/she is speaking has delayed too long in doing something. It is generally said with an exasperated tone of voice (even if the exasperation is somewhat in jest).
It also generally implies that the other person (i.e., the listener) has not acted because of fear or doubt, and that excuses have been made.