An inside mount is when blinds or shades are installed inside the top of the window frame. The window treatment brackets are either screwed into the 'ceiling' of the window opening or sides.
Blinds let you keep the sun out (and also stop internal light from escaping) which might mean the difference between you being able to sleep at night or not; or even the ability to see your TV screen for daytime viewing or not.
Thankfully, room darkening window shades can help you fall asleep and stay asleep by reducing the light that comes through the windows. Blocking out light at nighttime is important because it affects your circadian rhythm.