Calculation groups vs field parameters for time intelligence switching: what has worked for you?

Thanks v-achippa​, maruthisp​ and ShafiUllah-bc​. Wrapping this up with a summary for anyone who finds this thread later:

Default choice: calculation groups for reusable time intelligence (MTD/QTD/YTD/PY/YoY), since one set of items works across all base measures instead of multiplying measures.

Format strings: keep the base measure's format for value items and only override for ratios:

-- Format string expression on value items (YTD, PY, ...)
SELECTEDMEASUREFORMATSTRING ()

-- Format string expression on YoY %
"0.0%"

Performance: roughly the same either way, since both end up running the same DAX. The base measures matter more, so compare equivalent visuals in Performance Analyzer rather than assuming one is faster.

Multiple calculation groups: set precedence deliberately (e.g. time vs currency conversion) and test both orders against numbers you already know before go-live.

Self-service: field parameters are easier for business users to understand in the field list. So the split is roughly:

Reports built mostly by the BI team      -> calculation groups
Many business users building their own   -> field parameters (or friendly measures on top of the calc group)
Either way                               -> clear names + a starter report

Thanks again, everyone!