The "What"
Improving the timer feature of the iPhone clock app (Default app)
The "Why"
Because when exercising, especially high intensity interval training you need to follow and stick to timings.
In this case, I would love to use my iPhone while training since I am already carrying it with me wherever I go, it can provide more assertive timings to my daily workout.
I believe more people would use it while training if this feature was built, and it would be nice to empower people to exercise and improve their lifestyle.