What rooting does:
Rooting your phone does a number of things. It lets you get Superuser access to your root directory (where you can customize things like appearance or performance). It also allows you to flash(flash is rooting terms for install) a different kernel, optimized for the ROM of your choosing.
ROMs: ROMs are what I referred to earlier as the developers overtime. They create their own version of Android, a new Operating System, that customizes your smart phone experience. It can change the color of your icons, change the app dock, whether or not you have an app menu, etc. It can do basically anything. With a ROM you can uncap the full potential of your phone.
After ROMs there is apps: There are a number of apps on the market that only work while rooted. Screenshot apps, overclocking apps, etc. Just by rooting you are able to do so much more in the Market.
Speed and performance: Kernels are the things that tell your processor what to do, and how to do it. By changing that, you can change your processor speed and voltages. Meaning you are able to do what you love to do, only faster.
Looks: If you have the latest and greatest Android smart phone, you can’t deny wanting eye-candy. It’s your desire, and the reason you enjoy Android so much. When you root, you can take any imperfections out. If you think it would look better with a blue theme instead of a green one, or you want your favorite color everywhere, you can do it. If you don’t like the default layout of the phone, or the styling, you can change it too. You can even make it look like an iPhone. (Though I wouldn’t know why you would.)
Customization: This ties into the looks and speed and performance sections. Being able to say that no one around has the same phone as you is nice (iPhone users reading this don’t know what it’s like). But the moment when you do see someone with your phone, and you can still say your phone is different, is priceless. It gives people warm fuzzies inside.
Now that you have read that and know that you want to root, what next? This is the part where you head over to XDA Developers, go to http://www.xda-developers.com/ . From there, you can find guides on rooting, installing ROMs, and tips and tricks. The best ROMs are the ones that people try to port like MIUI, Cyanogen Mod, and others depending on your phone.
There are two main disadvantages to rooting and Android phone:
Rooting immediately voids your phone’s warranty-Once rooted, don’t try to bring your phone back for service or warranty work. You are on your own!
Rooting involves the risk of “bricking” your phone-In essence, a “bricked” phone is no better than carrying around a brick in your pocket. The phone is dead when it has been “bricked.”