By experience, the quickest way to summarize data with SAS is by using PROC SUMMARY/MEANS with CLASS.
Can't see that any EG tasks that is using them though.
My first guess would be that TABULATE (summary tables task) would use the same algorithm, but I'm not sure.
Apart from different grouping algorithms between SQL group by and SUMMARY CLASS, is the ability to specify ID columns,
in case where you have a set of columns that forms a hierarchy, no need to build summary groups for all, just for the level with finest granularity.
If your data is already sorted, PROC SUMMARY with BY is the most efficient way to summarize.