The only time PowerApps slows down is when it checks for errors. It does this when you are typing a formula and you temporarily break a variable that is used somewhere else:
Image1.Visible is set to a boolean context variable, "ShowImage."
You have the formula for ShowImage in one location:
You decide you want to put the formula in a second location:
As you type true/false, you break the original formula and PowerApps stalls as it tries to recalculate things. If it's just one formula referenced in one way, it's no big deal. In fact, you could probably copy+paste to avoid the issue altogether. My example is very simple though, but apps can be very complicated so breaking the formula is costly when you have to wait through it all.
So users of PA end up typing their formulas somewhere else, then copy+pasting it back into PowerApps. But that's so counterproductive since PowerApps has color coding and autoselection in its formula editor that you miss out on so many key features when you write formulas elsehwere.
I am suggesting a way to toggle the error checks while you type a formula so that you don't break things. Think of it like the DelayOutput property for TextInput fields. Is this possible?