@Atanas5CCF
Neither is "proritized", and you misunderstand the way this works. It's just a matter of capacity. If you're working with big files, there is no such thing as "enough memory". Total memory requirement will always exceed that, often by orders of magnitude.
The scratch disk is Photoshop's main memory. Everything goes there, all the time. RAM acts like a fast access cache, the content gets shifted and moved as needed. Switch to another document, for instance, or go back a while in history, and RAM contents immediately needs to change. 50 history states, each potentially adding the full file size, for several open documents - it has to go somewhere, and you need to have immediate access when needed.
This was critical in the old days when we had slow spinning drives. Today, with ultra-fast generation 4.0 NVMe drives, the speed difference is not really significant. I'm sure you still get measurable differences, but in practical use, it's insignificant. You're simply not able to press the buttons that fast - the machine is waiting for you a lot more than you are waiting for the machine. In short - the bottleneck is largely gone.
And there's one more crucial thing about the scratch disk that you're not seeing. It's what enables Photoshop to work with virtually unlimited file sizes without choking the whole system. Photoshop can handle anything you throw at it, and as long as you have enough scratch disk space, it won't miss a beat.
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