Waze tells you about real time traffic and dangers in the road (Like Potholes and shredded tires). a Garman GPS doesnt do that.
I started using Waze for this reason as I thought it would be helpful. Over about a month of use I could not find one instance in which the warnings were actually helpful. I just found it to be irritating and cluttered.
The worst is when people report potholes on the BQE. I could be sitting in California and tell you that there are potholes on the BQE.