Not enough RAM

Starting with macOS 10.9 (Oct 2013), Apple changed how RAM is accessed and used. In Activity Monitor the new metrics are Memory Pressure and Swap Used:

Note in the example that 11 of the 12 GB RAM is "used" but the computer was having no issues. Pressure in low in the green range and Swaps are zero.

I don't think it is anything that matters.

See Check if your Mac needs more RAM in Activity Monitor - Apple Support

including the information on memory pressure and also the following excerpt:

When you have free or unused memory, your computer performance does not necessarily improve. macOS obtains the best performance by efficiently using and managing all of your computer’s memory

Free memory is unused.

Free memory is wasted memory.

Free memory means having paid for something, and not getting value from that.

Memory can be used for I/O and app and other caching, which speeds subsequent access.

I’d question the operating system caching policies, if an OS can’t find some data to cache on a moderately-active system.

There are apps which purport to clean caches, and which can then degrade performance, as data then needs to be re-loaded.