Well, anyone with a camera with lens threading for filters, anyway.

Why? Glad you asked! There are two major reasons, while professional photographers may have more.

First - protection! You probably dropped a good chunk of change on your camera, and you want to protect it. Other than water, the exposed lens can be the most susceptible part of your camera for accidental damage. A scratch or chip on your primary lens will make it next to worthless. A UV filter in front of your main glass can absorb any accidental hits without damaging your primary, and is a lot cheaper to replace than your lens (or complete camera, if it has a fixed lens).

Second - picture quality. Excessive UV light can ruin the best planned shot. Indoors under florescent lighting you can get very poor picture quality. A UV filter knocks most of that out of the picture. Outdoors, especially near water or at high-altitude, excessive natural UV will push your pictures into the blue end of the spectrum - and you don't want that either!

This is a reasonably priced, quality, glass UV filter. Threaded on both sides so you can add additional filters if your shot requires. Well packaged in a solid case to protect it when not in use. With care, this should last for quite some time. Comes with a 2-year warranty, so don't forget to register it!

And always carry a spare..... just in case.