A long time ago I asked about this. Wiki tells us that it was designed a long time ago as a very economical filesystem - the design team included Linus Torvalds. I gathered also that it was included in Debian, and then in Ubuntu, so that's why it's in Linux. It can be seen during the install process, and is often among the updates if you watch what's happening.
Why? It only appears when a boot process fails, and I haven't been able to discover anything useful that can be done with it in that situation.
Does it have a behind-the-scenes value in other processes? Is it called by scripts? It would help general understanding if we could know a bit more about it.