When do I need to backup the Service Master Key? I'm reading some documentation and whitepaper about Transparent Data Encryption. Some documentation mention to backup the Service Master Key as well (For clarification I'm not talking about the Database Master Key). I just don't exactly understand why this is necessary, because I was able to backup/restore a Database with TDE Encryption from Server A (backup) to Server B (restore) without using any Service Master Key.

In what scenario do I need to restore the Service Master Key?
If you are talking about the SQL service master key, then there is a rare occurrence where you really need to restore it.  

I'm thinking of a couple of scenarios where you need to restore the SMK...  


Somehow it got corrupted.  
You are rebuilding your SQL server and planning to restore every database including system databases from backup. Usually in this case also you might not need to restore the SMK if you are using the same SQL service account and password.


In TDE you don't need to restore the SMK. As everyone said, you just need the certificate and the private key. You don't need to have same database master key, also as when you create the certificate from backup it gets encrypted by the DMK of destination machine.