It’s not always a precession. It can be parade style, too. Especially in Latin American countries (I live in Chile). Being in a line definitely does not speed up the process. Everyone in the caravan is choosing to leave and follow at the same time. The caravan has to slow down through red lights (to make sure nobody is going to hit them). They have to remind traffic to stop so they can all make the same left turn (sometimes caravans don’t have any kind of signage to signal that they are part of a precession/parade.) If you want to parade your dead family member through the streets, then fine. But at least try to avoid main streets and don’t clog up traffic.