It may be hard to imagine on the development side, but there are instances where a deployed host is not accessible from the Salt Master in a production environment. This forces a bit of creativity if you have a set of standard formulas you need to apply to the host.
For instance, imagine a host sitting in a highly restricted DMZ network. Even with the advent of Salt SSH for minionless administration, SSH access may only be opened from a jumpbox and not the Salt Master itself. In cases like this, a Masterless Minion is a viable alternative.