Currently it looks like PowerApp will do real time execution as any formula change. In my experience, it significantly hurts the PowerApp performance and many cases, my computer is like in slow motion, the keyboard and mouse will not respond. As I am using the highest model of Surface book, I shall assume other developers may even get worse system performance. My suggestion is to allow the developer to turn off the real time program execution while he/she is doing update to the program. That should improve the system performance. Thanks.