Necessary? No. But some of us enjoy creating a more, full world. A world where there are shopkeepers and strays, wanderers and friends. Its world development... Or would you rather pretend there are no shopkeepers or other rescue groups and we're just a batch of random pokemon in an uncivilized area puttering about on our own? lol

Personally I think roleplays without extras are about as good as a video game with no NPC's.