This file is created on a system crash, it will be quite large depending on your settings, possibly as large as your memory size. Depending on why the crash occurred it could be possible that a virus was in memory and not that is being detected.
This file is only of use to those with the tools and experience to analyse the memory.dmp file (to try to find the cause of the crash), so unless you have someone you know with the tools and experience then this file is worth very little. The older the file is again its worth is diminished further.
If that file existed when you had another system crash it would be overwritten, if it wasn't there a new one would be created, so it is a win, win situation, with no real downside having deleted it.