For simple cases, it is probably a total overkill to even consider it, but for something heavier, embedding the database gives you a chance to trivially migrate later to a separate database server.
Redis is not a database. It’s a key / value store.
It kind of is a database:
A key-value database, or key-value store, is a data storage paradigm designed for storing, retrieving, and managing associative arrays, a data structure more commonly known today as a dictionary.
that's still a database.
it's not a relational database.
you are confusing redis with memcached