Google, the maker of the Android Operating System for mobile devices, and device manufacturers, such as Samsung for example, provide you with a powerful device that is basically a tiny personal computer. However, unlike the personal computer you purchased, these companies do not give you full access to your Android device. They have the device locked down so that there are only limited things you can do, and limited things you can see on the device. It is your device! You paid for it! Why let big companies control something that you own? It is like Big Brother Government controlling your life, which is fine for some folks (like liberals) but for the rest of us, we want the power and control of our property to remain in our hands. Well, if you root your Android, you are taking back control and gaining access to the entire file system, and all of the capabilities possible with it.
By gaining root access you can modify the device's software on the very deep level. Alternatively and to be fair we can take a closer look at why your Android has been locked down with strict limitations. These limitations are said to be safety mechanisms put in place for security and to ensure that novice users don’t mess up their devices. On a Microsoft Windows XP computer, if you have Administrator privileges you can delete your c:\windows directory and render your computer inoperable until serviced (by reinstalling the OS). When you delete something important on your Android file system, it may not be so easy to restore it.
Some of the limitations are to protect you from doing things to disable the device. Other limitations are profit driven, such as those that encourage you to use the Google Play Marketplace, and prevent some 3rd party software functionality. Relatively smart individuals, and those even semi techie find these limitations a nuisance. They obviously limit how they get to use a device they own. Rooting is how users can lift these limitations and use the device the way they want to and not necessarily how the manufacturer wants them to.
When you root the Android device, you gain what is known as "Super User Privileges." Once you root your device, you will be able to use software that is more powerful than the stock apps and in the process you will have much more control of your device than you would without rooting.
Some examples that I personally enjoy since rooting my Android include the ability to install Samba so that I can share my Android drive on my Microsoft Windows network. I can install VNC Server on my rooted Android so I can see and control it from my desktop computer. I can also change annoyances about the UI such as disabling the stupid Google search button and an annoying side button that causes me grief. Finally, I like to remove Verizon apps (bloatware) that I will never use, yet Verizon locks onto the phone. Any of these carrier forced apps can be removed once you have root. These are just a few small examples of things that can only be accomplished after gaining root access.
Rooting is basically achieved by exploiting a security flaw or glitch in the Android software and installing a special application to manage requests for elevated permissions. It is similar to using the 'sudo' command in a Linux/Unix environment. The manufacturers consider root access a major security issue, as it practically opens the door to unwanted access, data leaks and theft, hardware failure and so on, if the developer has malicious intent. This is because the user can unknowingly allow a rogue app to gain permission to the operating system in a way that exposes the user's data. The user can avoid this by understanding and knowing what is going on, and not accepting permission requests without knowing for sure what those requests are for.
Root + Naive User = Disaster
Most manufactures will void the warranty if you root the device. This isn't to say that you are guaranteed to not have your device covered by warranty just because you rooted it, but it is to say that if the manufacture knows you rooted your device, you will likely have to kiss your warranty goodbye. Most of the root processes out there offer a backup and restore capability, so you can "unroot" your device (if everything goes correctly.) Also, a device that fails in such a way that no one can tell what is on it, rooted or not, can help keep your secret, that is, that you rooted it.
Rooting is not for everyone. The difficulty in rooting your device can vary depending on which manufacturer, model, and update you have. It can be mildly difficulty to extremely complicated to root your device. My Motorola Droid Pro is somewhat complicated, because I had to roll back the software version to an earlier one, something that is risky enough, before I could root it.
Experienced Android users may find the process of rooting Android as simple as installing an app from Google Play. Beginners, however, may find themselves in a pickle, having to deal with some not very straightforward procedures. The step by step process often doesn't go as described. Due to variances and glitches, you may have to make a quick decision to keep the process going. One wrong step, and your device is rendered useless. It is said to be a "brick" when the device is rendered useless in a way that it cannot be recovered. You can potentially brick your Android in the process of trying to root it.
A set of instructions for how to root your device may be dead wrong. When rooting users basically have to have blind faith in the developer responsible for the tool or the app that is/will be used, hoping that there's no sneaky backdoor built into it or that it will not harm the device. If you are using a rather obscure way to root your device, you are taking a bigger risk. It is a good idea to find instructions from multiple sources and compare to see if they correlate.
I have performed jailbreaking, rooting, hacking, and modding of Android devices, wireless routers, video game systems, and even some obscure industrial embedded systems. Typically, everything goes just fine. Sometimes I have had devices that no longer behaved entirely predictable, but that typically resulted from what I did after I had full control. It is what you do with your Android after you have root access that may do the most damage.