In theory, it can still be usesul on that same turn a creature Ready the Dash action, if it was able to move somehow without using its own Reaction, it could potentially gain the extra movement. For example, an Adult Black Dragon could upon taking its Legendary Action: Pounce following a readied Dash then moves up to 60 feet.
I suppose that would work as long as you trigger the Dash first.
Why so? Typically, you deduct the distance of each part of your move from it until it is used up or until you are done moving, so i believe the effect of the Dash action can happen at any time on the turn so long as you aren't done moving i guess. Don't you agree?
Yes and no.
First, I read the Pounce action more closely and Dash doesn't affect it. Dash increases your movement (a resource you normally have on your turn). Second, Pounce explicitly says the Dragon moves up their Speed. Dash doesn't change Speed and therefore doesn't affect Pounce. As an aside, the action is after another creature's turn so technically, they are in a between turns limbo. There may be some weird rules interactions with that timing that I can't think of right now. I think there was a third party or homebrew feature that gave a reaction on every creature's turn for use with that feature, but if that exists, it's off topic for this discussion.
Second, you don't have to Dash before you move, but if your Speed is 30, you have to Dash before you move that 31st through 60th foot. In the case of the Pounce, if they worked together, you fully move and attack within the Pounce, so the Dash re/action has to come first.
Yes and no.
First, I read the Pounce action more closely and Dash doesn't affect it. Dash increases your movement (a resource you normally have on your turn). Second, Pounce explicitly says the Dragon moves up their Speed. Dash doesn't change Speed and therefore doesn't affect Pounce. As an aside, the action is after another creature's turn so technically, they are in a between turns limbo. There may be some weird rules interactions with that timing that I can't think of right now. I think there was a third party or homebrew feature that gave a reaction on every creature's turn for use with that feature, but if that exists, it's off topic for this discussion.
Second, you don't have to Dash before you move, but if your Speed is 30, you have to Dash before you move that 31st through 60th foot. In the case of the Pounce, if they worked together, you fully move and attack within the Pounce, so the Dash re/action has to come first.
How to add Tooltips.
My houserulings.