IMO, you nailed it. Outside, while it does cancel throw, is not the reason it is used most. Outside is running english, which means you can move the cb farther at a slower speed. You don't have to force the cb. It is a more natural way to get position.
That said, you use what ever english you need to get your position. You try and play position to use outside.
I believe you have this wrong. Running english occurs when the cueball is spinning in such a way that the spin is condusive to making the cueball travel faster upon hitting the rail.
Let's suppose you are cutting a ball to the right at a 45% angle, but you use side/right english. This is inside english, but when it hits the rail the cueball is spinning counterclockwise, which is running english as this spin causes the cueball to travel faster as it hits the rail.