What are rodcs? and what are the major benefits of using rodcs?

RODC is an abbreviation of Read only domain controllers. As it name shows they are read-only. RODCs are actually used in small branches where you have less personnels and usually no or person with less IT knowledge to administer a DC. What it does is when you have replication configured on different sites and each DC is replicating all of the objects etc to other DCs, that is actually a security risk. Where you have only a number of person in a branch and you are getting the usernames and passwords for all the employees of your company to your that small branch DC and some one just steal your DC and by doing some small effort takes out your all credentials, thats not fine. So RODCs only allow you to limit what specific objects you want to replicate to this small DC and if you loose credentials in that case that would only be of that specific branch. Less security risk. Hope it will help

Read Only Domain Controler (RODC), useful if you need to have a child domain controler at a less secure location, RODC's can provide authentication to local users if the external network(internet) is down, but you cannot add remove new users on it (read-only)