There are many times when the design intent for a pattern is where the original member is the 'center' of where all of the members should be. This is more for the directional/dimensional pattern type. Using mirror doesn't work well for a few reasons:
1 - the original member would be repeated twice
2 - mirrors don't always update and propagate well (especially with holes)
3 - mirrors prevent reference changes to the base feature.
Setting up a directional with a rotational pattern also doesn't always work well.
We would prefer to have a toggle where the direction of these patterns are simple - Direction 1, Direction 2, Centered (or uniform).