MR is popular on clouds — offered by AWS/Azure/Google.
I used to question the validity of on-demand/rent proposition. I felt during a peak period everyone is busy and in an off-peak period everyone has low volume. Now I think Hadoop is a nice example.
It often runs for a short time but involves many compute nodes. This could be in a off-peak period. Without cloud, the Hadoop will have to make do with much fewer compute nodes.
Further, any batch job in general could be scheduled off-peak.