basic use of dbfilter is

you don't have to choose or create database every time

you can't choose database while you restart after DBdrop. that will be a disadvantage (it work with the same dbname every time) 

basically, it makes your routine work faster, nothing else

Please read the documentation carefully, it is exactly described. You need dbfilter, when you are using public websites AND hosting multiple databases in your Odoo instance. dbfilter maps the hostname of an HTTP-request to a particular database.

Example:

HTTP-request: https://www.example.com/shop

Hostname is www.example.com in this case.

dbfilter defines the database name to be called (for example "example").