Rooting refers to taking a packaged product, which typically runs Linux, and somehow modifying it to allow you to log into it as a normal superuser "root". Many Linux enthusiasts get excited over the common fact that their dvr, tv, blu-ray player, mp3 player, video player, satellite/cable box, router, wifi access point -- oh and phone -- runs on Linux, so they think, "How can I login and issue common linux command line commands, and become root, so I can do whatever I want?"

Notice this purpose is strictly exploratory, but some projects have taken advantage of this idea and offered up third party firmwares for specific hardware. These different firmwares reprogram the OS for your device, they may offer new features, but they also may be buggy and some features may not fully work, yet.

So to answer your question, you may want to do it if you're interested in how your device work, and taking a risk on reflashing the firmware on your device, to a custom mod, or firmware. How you weigh and define the risk is up to you. There are specific sites out there for specific hardware (phones, routers), and entire communities built around custom firmware for model-specific hardware.