Performance of coroutines in mobile

There's no difference in performance to when you're using coroutines in a PC or Mobile. Coroutines are basically a method that can be paused for the time of whatever yield instruction you pass to it.

The only difference you may see is that the impact of a bad implatation is a lot more noticeble in low end devices. Further more i would say that a wise implementation of coroutines will give you a performance boost especially on mobiles.

I great read to understand how to use coroutines is: http://www.theappguruz.com/blog/how-to-use-coroutines-in-unity