Is there a step by step guide on how to use the Add version formulas to line item subsets in module blueprint ?
I don't see any line item in the left box.
I assume you mean applying version calculations to line items, vs line item subsets.
In any case, depending on your use case, I'd say you're better off using a boolean line dimensioned by version to determine what calculation to run.
E.g. IF List Attribute - Version.Version = Actual THEN X ELSE IF List Attribute - Version.Version = Forecast THEN Y
Gives better auditability of your logic, is likely more maintainable and gives you the flexibility to group logic (e.g. if multiple versions use the same calculation, you can have a boolean that triggers the same calculation for all the like-versions).
The performance implication is probably less clear, but will depend on your usage.
You might want to read this best practice.
Line item subsets demystified - Anaplan Community
I owe the article much.