I've had to have it done after each birth (all in completely different hospitals), but they have always explained what they are doing as they are doing it. It is to slow down the bleeding and stimulate the uterus to contact. Sometimes it hurts more then others, but they really do need to use a fair bit of pressure. I have been warned by my midwife this time (again a different hospital) that they will likely need to do it after I have bub, particularly as it is my fourth baby and I have quite fast labours.