We personally feel that rules are meant to be broken, but in this case we recommend using some type of window treatment the vast majority of the time. An exception would be if several of the following points were true of the space...
• The windows are in great condition If they're not cleaned often, if the paint is chipping around the edges, if they are unsightly in any way, you'll probably want to not see them from time to time, right?
• There's a great view Be it a lovely view of the woods or a city skyline, the view has to be good (like, really good) for you to forgo window treatments.
• The windows are in a public space of your home Bathrooms and bedrooms require some type of covering - period.
The windows aren't facing East Because you don't want to be blinded by the sunrise when you get up to make coffee in the morning. West facing windows can be okay, but it depends on if anything is screening the sun through the afternoon, such as trees, etc. Basically if you find yourself squinting a lot, that's reason enough to invest in some window treatments.
Do you have exposed windows in your home? What makes them work? Any guidelines you'd like to add?