Sunglasses are powerful since they can be used as both tools and fashion accessories, and since that they can utterly fail in either role if used improperly.
Sunglasses are really amazingly useful, providing all kinds of benefits to those that wear them. Not only to they protect your eyes from all kinds of shit that will make you go blind (Something about the sun, and rays or something. But really, don't bother me about doing actual research. It's much less fun. Honestly, if you care, google it or something.), but also they further the advantage of the modern fisherman over limbless vertebrates who are easily by shiny things and can be fooled into biting food covered hooks.
Furthermore, sunglasses can enhance one's cool factor. It's a matter of some debate as to whether it is because sunglasses posses large quantities of the Selleck Particle (named after famed badass actor Tom Selleck) that they can achieve such a high coolness factor, or if it's simply a matter of simian mimicry of the rich and famous that drives sales. Many examples of sunglasses increasing the relative bad-assesery can be found in Hollywood. Most notably: Men In Black, Top Gun (Ignore the volleyball scene for now and focus on the glasses), The Matrix, and Cool Hand Luke.
Maddeningly, sunglasses can instantly arouse great feelings of hatred amongst higher thinking beings (such as those discerning readers who spend their days perusing the brilliantly written articles of sites such as this one) who see them being worn indoors, especially at night. No real cause for such behavior has been discovered yet by the team of dedicated researchers here at Cracked, but the leading hypothesis is that overuse of tanning beds causes day/night confusion and paranoia at being looked directly in the eyes. But more on current douch bag theories can be found elsewhere.
However, a small exception to indoor sunglass wearing can be made for those who practice the fine art of poker, where a fine pair of sunglasses can help disguise the elation many feel at being dealt pocket Aces.
Some things to keep in mind about the use of sunglasses:
The kind of sunglasses you wear DOES matter. Some ARE cooler than others. (It may help when purchasing to check the Selleck Particle number on the frame.) Also, there are some people that even sunglasses can't help.
"Opponent rolls 20 Basement Dwelling. Sunglasses Ineffective."