Now many of you people wouldn't know what 'Root' is so, lemme explain, it is kind of a 'Privilege', which allows us to access the core functions of our android smartphone, it is something that is not allowed by the smartphone companies and what they do is if they find that a phone is rooted, they void it's warranty because it is something that could help us overlock our phone's CPU to a higher level.
Now this is only one feature of root, but there are many others like by rooting your phone you could have access to 'Cheat Tools' which can help us modify an apps data, make In App Purchases (IAP) free and patch some apps to get their premium versions for free, removing unwanted system apps with ease, but it also helps in SECURING OUR PHONE, like '360 Security', it needs root to establish a firewall to protect our phones from unwanted access, key logging etc., I think that it should be allowed by the smartphone companies, like there are two sides to every coin, just like that, there are two kind of people, one which need it to secure their phones and one who hack IAP and stuff by using it.
I want to say that people would never stop rooting their phones and hacking stuff just because these companies void the warranty, it's like a limitation, how do you know who will use it for the good and who will use it for that bad? So, simply just let people do what they want, they paid for the phones and warranty comes within it.
Some tools that could help you root your phone:
(Mobile)3) Unlock Root
(PC Version Only)4) Framaroot
(Android version only)
Some hacking apps due to which smartphone companies don't allow root:
2) Lucky Patcher
3) SB Game Hacker
Note: I've not posted the rooting methods, please search Google for that.