Maribor’s public transportation system is reliable enough that a car is by no means needed. This even extends to visiting the Pohorje Mountains that are a 15min bus ride from the city centre and then only a 10min cable ride to the very top.
However, having a car can be useful if you don’t want to rely on the schedule of the buses or if you want to visit Maribor’s nearby wine roads. Parking is also free in Maribor on weekends.