I am sure i have heard strong opinions like this but in practice joins are never cheap, tables with billions of rows crossed with millions of rows just to find a single row with data is not something i would call cheap, more often than not it is better to avoid joining large tables if you can live with duplicate data, also one trick i have found better is just to archive data in your tables which are not accessed frequently and reduce the size of tables keeping only the data which is needed
I am sure i have heard strong opinions like this but in practice joins are never cheap, tables with billions of rows crossed with millions of rows just to find a single row with data is not something i would call cheap, more often than not it is better to avoid joining large tables if you can live with duplicate data, also one trick i have found better is just to archive data in your tables which are not accessed frequently and reduce the size of tables keeping only the data which is needed