Genus Synthesis - Cost Groups

I came across a statement in some training videos that understanding how to effectively create cost groups in a design will aid in achieving the best results. The default for Genus is to create separate cost groups for each clock in a design, but I am going to have to do some weird things earlier and need to know how to create my own cost groups in a manner that Genus still is okay with. Therefore, my question is the following: where can I find documentation that explains how to properly configure cost groups, as well as explanations of what the cost grouping/path grouping tool is used for. I cannot find anything on the website or on the internet about this even though Cadence emphasizes it as important.