You use 저겨 mainly to call somebody's attention (a waiter, a sales person, a passerby etc). 실례합니다 you are excusing yourself for disturbing the person and taking some of her/his time to answer your question. So if someone is not looking at you or is doing something else you would say 저겨. After that, it is good manners to start by saying 실례합니다 before stating your question. If the person is already looking at you and knows that you are going to ask a question then there is no need to call his attention. In that case you would not use 저겨.