After installing FancyCache I've stumbled upon occasional high CPU usage in System process, sometimes even for a few minutes, apparently when I do some heavy stuff like photoshopping a huge bigboard or searching text in 100000 files (this was also happening with SuperCache).
I just thought what if this may be prevented for example via specifying a list of applications for which FancyCache shouldn't cache disk-writes or disk-reads. The prime example seem to be disk defragmentors. But actually it's not uncommon for apps that process video or audio files to write 1000 GB of temporary data when you work with huge files, also these apps usually have their own memory management and write to disk only because it's impossible to hold data in RAM.
p.s. Actually I have to take my words about disk defrgmentors back - all of them write to disk immediately out of reliability concerns apparently, but if you have an UPS then FancyCache HUGELY speeds-up the defragmenting process with its delayed-writes-combining feature, thus giving a phenomenal speed boost and a much lower HDD noise level.