Drive through any neighborhood developed in the mid-20th century, and you'll likely see more than a few storybook homes with fake wood shutters framing the windows. These were meant for decoration and to make the homes look cute, but the shutters were also completely and permanently stuck to the exterior of the house. If you're remodeling, you have a chance to get some real wood shutters that you could actually use to protect your home's windows.
Protection Against Weather
The real reason to get external, usable shutters is to protect your windows. The shutters not only block rain but also provide an extra layer between the glass and things like hail. Severe hail -- the stuff that gets compared to various fruit and sports ball sizes -- could still likely bust through the shutter and glass unless you get impact-resistant materials. Moderate hail may still damage the shutters. But a damaged shutter is a lot easier to replace than cleaning up broken glass.
Blocking Sunlight While Allowing Air
Shutters act as sunshades. On nice but bright days, you can close the shutters so that direct light is blocked, while the window stays open and lets air in. Most shutters allow you to move the slats like you could on mini blinds.
Mildew Potential and a Solution
Shutters that aren't going to be sealed completely against the house need to be set a few inches away from the siding. If you place the shutters right against the siding and don't seal everything up (which you can't do if you actually want to move the shutters), then you risk bugs and rodents moving in. The space behind a shutter provides wonderful shelter for local bat populations. You don't actually want that in your house, though. The solution is to ensure there are a few inches of space that allow wind to pass behind the shutter, making the area uncomfortable for shelter-seeking pests.
Do be aware that if you want to be able to access the shutters from inside the house, you'll have to modify your window screens. The typical window screen can be pulled out, but it's a pain to reinstall. If you want to keep your plain window screens, you'll need to go outside to latch the shutters, something that's not possible for second-story windows. But some screens have cutaways in them -- like little doors -- that allow you to access the shutters.
One of the real problems that those cosmetic shutters had was that people never really took them seriously. The shutters were kind of the subjects of mild jokes since the shutters were pretty much useless. But adding real shutters that you can move and latch together adds some curb appeal to your home. Now you have shutters that look real because they are real, and that is a point of interest to many home buyers if you ever plan to sell the house.
So check out shutter types and see what's available to you. If you noted that many of the issues mentioned here would either benefit you or not be an issue for you, then getting usable shutters could be a very good idea. Contact a company like The Louver Shop for more information and assistance.