I use some cameras that either don't have a viewfinder or the viewfinder isn't very accurate. I'm a big fan of viewfinders in general, but I'm not afraid to go without.
I once heard a story about a student of Garry Winogrand asking him about shooting from the hip, and Winogrand lectured him that the viewfinder was vital.
I think it's possible to learn what a certain lens is going to see; maybe not 100% accurate, but good enough for many subjects.