The Capacity Metrics reports will show Monthly usage in WLM and Service Level Classes by MSUs consumed.
For example; if you collect the SMF 70.1, and 72.3 records for a long period of time, the report generator will break down the graphs to monthly views. Plus, some of the graphs will break down the views to LPAR level.
A person does not have to run 1 long SMF extraction job, but can run multiple jobs to gather the data, then when creating the Metric's report select all appropriate input csv format files. This will create monthly snapshots of your system's usage.