It can happen in any circumstance where the police (or, more likely, the CPS acting through the police) need someone to attend court to give evidence. That person might simply be a witness to a crime but they could also be the victim. (I received a witness summons after my car was stolen).
A summons has no legal validity until it's in the hands of the person who is being summoned. That's why they are usually delivered in person, rather than by post, so that there can be no doubt that the recipient actually handled it.
Police officers don't want to 'play at postmen' all day long, so the delivery of summonses is normally done when:
(a) the person is likely to be at home ; and
(b) it fits in with the routine patrol duties of officers in that area.
Chris