Is it good or bad to use an SQL temp table in Tableau/Power BI in the Initial SQL section? Would this improve performance or decrease it?

My last company relied upon Temp Tables for virtually anything analytical. Creating a dashboard? Temp table, every time. Huge temp table with tons of data, or we use a big ETL script with 5-25 temp tables strung together. We were not permitted to use any CTE or window functions. We did not have DBT or anything like that. Just write a 2100 line SQL query and hope it runs, test it for weeks/months.

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