You would get root access to your phone. Meaning you would have access to all the important folders, file, etc on your phone. With this kind of access you would be able to do many things like flash a custom recovery like twrp or clockworkmod. Which can be used for things like installing a custom rom such as Cyanogenmod. Cyanogenmod can improve phone performance by using less battery or ram. There are many different things you can do with a rooted phone I just listed what I mainly do with a rooted phone.

Thanks Bro A rooted Phone sounds good thanks :p

Yeah in most cases a rooted phone is way better than a non-rooted phone. Just be careful because phones can be finnicky and can be easily bricked by a small mistake. Though the process is usually pretty easy.

I can add a little bit to this but I have a rooted Galaxy S5 and its amazing. You have access to folders and files that you wont have access to with a un-rooted phone as he said above. Also there are a lot of cool apps that only rooted users can use. Video recorder, gamer hackers, mods, back ups, system changers... Stuff like that. Also you can do Custom Roms. I dont know a lot about this but it can increase the performance of your device and change the look.