One of my favourite instructors at UBC, Dr. Matthew, used to say this all the time and I think it is a very good advice. Here is a case that walked into my office a few weeks ago. A young female patient developed a very large and extremely painful swelling over night on the roof of her mouth. She had been in pain for a few days prior to the the development of swelling for which she had been placed on appropriate type and dosage of antibiotics. Tooth#25: previously treated ~5 years ago, crown came off due to long-standing leakage one month ago, cemented back on permanently, pain started 2 weeks ago, referred out by her dentist for re-treatment.
At emergency appointment, I&D was performed. For achieving appropriate and safe drainage, the tip of the blade should make contact with the bone and the incision line must be parallel to the path of nerve and blood vessels in the area. Rinse the area with saline and apply digital pressure with moist gauze. I personally do not place a drain in.
When the patient returned a week ago, she was comfortable and ready to continue with the initiation of re-treatment. Antibiotics alone would have not helped in this case and there is usually no real need for initiation of re-treatment at the emergency appointment.