What is the idea/benefit of having 'myself' as a beneficiary?

Having yourself as a beneficiary is brilliant in the case of a bad accident or temporary memory loss. If you do not log in to DieFi for X months, you will be automatically contacted (like any other beneficiary). You will undergo ID, face scan, and further security checks. When cleared, you can regain access to DieFi.
So you can use DieFi and have only yourself as a beneficiary. You don't necessarily need to register others than yourself. It's totally up to the user and can always be changed.