Windows aren't bad if you can have symmetry for monitoring in a mixing room. I mean, if you have window to your left side, you must have same to your right side, otherwise, after acoustic treatment, non-symmetrical reflections from windows will made a sense of something that may be called (frequency dependent) "broken stereo image", from my experience, some people cannot easily adapt to this.
In studio space you may build/buy mobile panels to block/absorb reflections from windows... or you may use (creatively) this reflections for recording... if you like.