[clutchski]

Because it will persist between restarts?

[hendzen]

then it seems strange to call it a cache.

[yummyfajitas]

It could be a cache to a much slower backend. I pull a lot of stock price and other data to my server which is is slow - 200-1000ms per series. I cache it in postgres which allows me to load it nearly instantaneously. It also allows me access to data while I'm disconnected.

Another reason to cache to disk is that you want to store more data than you have ram.