Issue about Time Settings and Roll Up interval

Hi everyone.

I have an issue about the feature "Series Roll Up" on a custom report.

Test 1 :

- the roll up interval = 1 month & Relative Date Range = Last 1 Months. The CPU Contention = 0.15 % on my ESXi. (see picture 01)

- Time settings "Relative Date Range" = Last 1 Months & the roll up interval = None. The CPU Contention = 13.44%. (see picture 02)

Does anyone know why? Do you know exactly what Roll Up is?

Thanks for your feedback :-)