IOS: To use shouldRasterize or not

IOS: To use shouldRasterize or not

I'm trying to optimise performance on my app, and playing around with
shouldRasterize.
I have a background view with a opaque subview on top. If I set the
subview to shouldRasterize, it turns yellow when checking the "color
offscreen-render".
If I have understand it correctly, you should try to minimize the
offscreen-render, but shouldRasterize normally increase performance on a
static subivew that won't change?
Should I keep "shouldRasterize" on or off here?
Thanks