I had an unusual experience when I demonstrated PS and ACR to a meeting. I had my laptop screen duplicated to the projector and had opened a RAW file in ACR at some stage before doing other things in PS.
I closed the lid of the laptop and when I got home and tried to open a RAW file, the PS blank screen came up and the laptop froze. There was a ding when I tried to do anything.
It took a while for the penny to drop and I attached a second screen and there was ACR still on the second screen when I extended the laptop screen reather than duplicating.
I seems that ACR still retained athe second screen redirection even when there was only the one screen available, being just the laptop.
This appears to be a bug to me as PS knew to display on the single screen but ACR does not.
I was lucky to have access to a second screen. But if I could not then PS would have been unusable for RAW files showing on the 'hidden' ACR on a pseudo second screen.