SYMMETRIC key & certificates role in sql server?
You are protecting agains accidental media loss (a lost laptop with the database, your drive showing up on a flea market with a copy of the database or of a backup) etc etc. Any scheme in which the processing itself (the database engine or the application) requires to access the data without the user providing a password only offer access agains media loss. The encryption key hierarchy is rooted on the system DPAPI encrypted key, in other words on the password of the service account. Such a scenario never protects agains a hacker that gets access to your SQL Server, and is not meant to protect such.

The alternative is to ask the user for a password each time it uses the application and use this password to open the key at the top of the encryption key hierarchy (usually a certificate in the database). This scheme is very seldom deployed in such cases as some multi-tenant scenarios when the tenants do no trust the hosting operations/administrators.