Every turn each character has move distance, an action, a bonus action, and a reaction (which can technically only be used while enemy is taking their turn). Dash normally takes an action and can't be used at the same time as an attack or any other action ability. At rogue 2, you get the ability to dash as either a normal or bonus action (but not both in one turn).
Normally: you can do the following in some combination: move 1x distance + attack + shove, move 2x distance w/ dash and jump part of it or shove but not attack.
With rogue 2 you can: move 2x distance w/ dash and still attack/scroll/cast in the same turn.
Sometimes you want to still use the regular dash instead of the bonus dash if you need your bonus for jump/hide/shove/potion.
