For newbies to Android world, this is a common question.
All this has to do with OS of the software. When you have rooted phone also called stock phone, you have the orignal software. This software has certain safeties which protects the user from making any changes which might damage the hardware.
Whereas in unrooted phones, the OS software is replaced with another modified one which allows you to play directly with the hardware of the phone.
If this topic of interests to you, you may need to research before you un-root your phone as unrooting should not be taken as childs play.
Keywords: Rooted phones, unrooted phones, stock mobiles, Android mobiles.