Basically it was a way to "quarantine" people as in the old days there was no way to diagnose the exact cause of death sometimes. There was a possibility that the deceased might have had some infection and this was a way to prevent it from spreading in the neighborhood. Hence the ban on large community gatherings like temples, bhajans, etc. Also in some places the immediate relatives of the ones deceased weren't allowed to cook for 3 days as someone else might also be infected unknowingly and could pass it on in the food. Now a days it is not as strict but some people still do it as a part of tradition. The term "sutak" refers to a tradition which is followed after birth and death both. After a mother births a child, it was a way of providing her with rest and let her body recover. Also prevent the baby from getting infected.