There is a possibility that some folks might be a bit claustrophic without the additional front windows. They help the cabin seem roomier than it would without them. They also improve the available light for reading, playing cards, etc.
The stock cabin curtains do a good job at keeping out light at all but the most obnoxiously lit campgrounds - mostly private campgrounds, but also some state parks, COE and a few others.
While laying down, you will only see straight up, so clouds and limbs are the standard view. But the window is tinted, so the view is better outside. I suspect their main function is natural light, since when you are sitting up in the cabin you are facing away from them.
We have had no leak issues with the front windows, and that is with our camper having been outside a lot in the past five years. With that said, we try not to linger in places that rain a lot... But we have had rain the past two nights.
I really can't think of a con. I've had truck bed canopies with similar windows and was worried about leaks with these, but they have worked great and we've had no problems with them.