Board Game Arena

I am confused on why I would want to use them. I know you can use 2, and they cost points, but why?

1. Greater flexibility in placing numbers. A roundabout splits your street into two streets, each half-street having the ascending order requirement. With a roundabout you could have two 1s in the same row, for instance.
2. Some plans require a roundabout.

In games that allow them, roundabouts are fundamental to victory at higher skill levels. If you check out a replay of top ranked players, you may learn that way. They also act as fences for completing plans.