Basically, parsing the percentages, using compressed data in RAM is ~1 order of magnitude slower to get into memory, and less than 1 order of magnitude slower to read from RAM. That is still around 2 (or more depending on setup) orders of magnitude faster than the hit to go to SSD / SSD RAID.

Useful knowledge on latency: https://gist.github.com/jboner/2841832

Because it's so much faster than having to go to disk.