RODC are used in non secure areas (Where the physical server can be compromised).
You can establish which credentials can be cached on an RODC (Computer and User objects).
When a user or computer authenticates against an RODC, the RODC will authenticate the user against a writable DC. If the object is allowed to be cached, the RODC will cache the credentials for future authentications.
Should the RODC server be physically compromised, you will reset all objects passwords which were allowed to be cached – limiting the attack foot print and impact on your organization.
Do not allow administrator accounts to be cached.
RODC should be placed near a writable DC (Near being the lowest cost site)
An RODC should not be considered as a resilient DC to a writable DC.