Well you can still watch true the viewfinder when you don't use LiveView, but then again what function is the field monitor having then, other then being a big thing hanging on your camera. Then just normal info is displayed on the monitor and you can use it to review pictures taken.
The zoom is contrast AF that zooms in on the subject, it is the same as with no fieldmonitor connected and you can see it on the backscreen of your camera (only K-5 has it). It has nothing to do with your lens.
I also use the screen to walk down a big pile of pictures when I got out to make a lot of pictures to select them.
I'm not that of an expert, I just have one