Premium Features
Android in original form is cool, but mobile vendors hardly think so – they try to improve it in terms of features and looks. Stock ROMs comes with lots of premium features which are not available in Custom ROMs (at least not for free). These features include custom home screen or launcher or app drawer, e.g., Sony Xperia phones have TimeScape UI whereas Motorola phones have Blur UI. For example, most Android phones come with keyboard with Swype feature using which you can type a word with a single tap on the touch screen by just swiping your finger across each letter of the word and keyboard automatically guess the correct word
Trust for Security
May be it feel strange but one can easily trust Android operating system sold by a reputed company. You can be sure that it does not contain any backdoor, malwares, spywares or other malicious tools. I’m not saying you can’t trust Custom ROM but it’s just that many people take their privacy on top of all other things – you can easily trust a reputed company you know but how can you trust a software or source code of unidentified origin or developer.
INU VS INS
if you are from India there will be two version of Roms INU and INS, these are product code, AKA region code.You can check it on Your device's salesbox or through kies. there is no major difference between INU ans INS Roms. the only thing is if You are on INU region you won't get OTA update of INS region release.same with INS.
Checking on Sales Box
Checking on Kies
just connect your phone to kies and it will show you the product code