Explain when would you use Joins vs. Blending in Tableau?

Join when the tables live in the same data source and share a granularity that will not fan out. A join happens in one query, gives row-level access to every field on both sides, and can be published as a single data source others reuse.

Blend when the sources genuinely cannot be joined — separate systems, or managed APIs like Google Ads and Analytics — or when the two sides sit at different levels of detail.

That second case is the one people miss. Joining daily transactions to monthly targets repeats the target across every day and inflates it. Blending aggregates each source independently before combining, so both figures stay correct.

The short version for an interview: *if the data is in one place, join it; blend when it is not, or when the granularities differ.*