Photoshop does not empty cache files until program is cloesd

The camera raw cache is supposed to remain. That's the whole point, otherwise there wouldn't be any need for it.

As for Photoshop, it's important to realize that the scratch disk is always in use. RAM acts as a fast access cache to the scratch disk's main memory. This way, most current memory activity can be executed in RAM, while scratch disk activity can be run in the background. With a fast disk and enough space, the process is streamlined and seamless.

There is no such thing as enough RAM, and there is no point trying. A scratch file can easily be 100 GB or more.

Memory is by design not released until you exit the application. Reusing it is much faster than re-requesting it from the operating system. You set allocation in preferences to ensure there is always enough left for other applications and system processes. Note that ACR runs in its own address space, so it needs memory outside Photoshop.

I think they intend for caches to persist until quit because the point of a cache is to load recently used data faster than going back to the original document and recalculating recent actions, saving time. And part of the assumption is that you might re-open a document you recently closed, so don’t dump that cache just yet. But it’s been recognized that sometimes Photoshop paints itself into a corner, in terms of memory, so if that’s happening, you can try choosing the commands on the Edit > Purge submenu. Those commands do purge certain types of items that Photoshop might be holding in RAM, but I don’t think we can assume those commands are a complete purge of Photoshop RAM.

If this happens a lot, it’s a sign that the computer probably doesn’t have enough RAM for the sizes and types of Photoshop documents that are typically edited on that computer. If free space on the system volume also gets low during Photoshop edits, that’s a sign that a large scratch disk needs to be assigned to Photoshop, or the system drive needs to be larger.