Spending a lot of time outside is a MUST in the summer (with sunscreen, of course!), and wearing sunglasses is a great way to protect your eyes from harmful ultraviolet (UV) rays, which can lead to the development of cataracts.
Personally, I love to be near the water, on a boat or a beach, or poolside, and the water can make a killer bright glare when the sun reflects off of it.
If the glare bothers you (how could it not?), then you'll want to get a pair of sunglasses that have polarized lenses. 
