This is the feature that was intended to improve the experience for using all 50 troopers each day.
The reason we went with this feature is that, as our game and our live events have evolved, we've felt that doing battles in various places (and in some cases with specific requirements, like the
Beckoning Nightmares event that is currently running) is one of the main kinds of activities in the game. However, because a some of these events are tailored with the amount of
time it takes to complete battles, we didn't want to add in something that completed battles instantly. Completing battles instantly discourages the value of creating teams that can complete battles quicker, which we think is a healthy goal for players to strive towards (which is why we've added things like clear timers and Relics).
In addition, doing this means that you're only best able to use Auto-Replay in levels you definitely have a strong handle clearing. This again creates value in people finding the right kinds of teams to quickly and consistent clear harder Lord of Light and Brave New World levels, and lets you use Auto-Replay in those features to better tailor your grinding based on the rewards you're looking to achieve.