It wouldn't be a matter of wasting time, it would be a manner of a person having to plan ahead before parking. If you want to park in a busy neighborhood, you may find that you can't actually do so for several hours, if others ahead of you in line have reserved those spaces. This is completely fair since everyone is treated equally, there is no 'wasted time' in this system that wouldn't have been wasted in the current system provided the spots are maximally full at all times. The current system results in some people getting lucky, others driving around in circles trying to find a spot, and others completely giving up. All of that time is being wasted. Beyond that the folks driving around are congesting the roadways, resulting in additional negative effects on the overall efficiency of allocating parking.

The main issue with designing a reservation based system is how efficient it is with regards to spots being continually filled, along with the constraint that it be considered fair by all participants. It seems like a design challenge but the current greedy algorithm probably sets the bar pretty low. It would be interesting to simulate.