...where you don't care if you lose the data. So data sets where you are getting a new version of the data every day and so if you lose yesterday's dataset you don't care.
also, datasets that fit on a single machine, rather than need to scale out over many machines, unless you don't mind the intrinsically broken "scaling" solution that is master-slave architectures.
Can you explain what you mean by "lose data". I don't know much about mongo, but I thought you could configure the client to wait for the disk write before returning.
