Is a procession / march on Mawlid an- Nabi a Sunnah or bid'ah?

Some Muslims who celebrate the birthday of the Prophet [saws] do a march (called a juloos) through their city on that day. If we were to accept that the celebration of the birthday of the Prophet is permitted, is it a good thing to do? If we accept that the celebration of the birthday is haraam, then obviously it can't be a good thing.