not necessarily, but it can be a good idea to have a distributed, tamper proof ledger of transactions.
that way anyone can provide proof for basically anything to do with the service: payment, drive, location, etc.
it might also have advantages from a security perspective for riders and drivers.
there are advantages, they're not entirely necessary, but they may well be the best option for a distributed network (i.e.: no central server infrastructure, at least not beyond some simple software repository for downloads/updates)