Based on my experience of a database where million of records are present and being operated for inserted/updated/deleted in a year. We were having proper constraints for data integrity purpose and there was no problem at all in intial time, but later on DML operations getting slower and reached to unacceptable level sometimes failed to execute. Then we removed the constraints to get performance back in the database.

Hence for SELECT operation definitely there is a benefit else DML operations will be slow later on based on amount of data.

Thanks