If you turn your phone off at night, then you're good. Turning it face down doesn't stop future sounds though. It only stops a sound that has already started. After that, if the phone rings or a notification comes through, it will still ring.
Blocking mode does a lot more than all of that though. It allows you to set a specific time period (like when you're sleeping at night, at work, busy with something, etc.) where you only want what you deem to be important calls to come through. For instance, I never turn my phone off during the night because I'm worried that I'll miss an emergency call. But I do get the occasional wrong number or drunk call from a friend that wakes me up for no important reason, and that's annoying. With blocking mode, I could set the phone to only allow calls from the people I'd be worried about missing emergency information from. That way, I still get the calls that I feel are worth being woken up for, and I don't have to be bothered with the calls that are nothing more than annoyances.