Intersect returns only members that appear in both of two sets. One example might be to show products that performed well both last year and this year, or customers that are both high volume and high margin. The default is to drop duplicates although “, ALL” can be added if these are required.

This example returns leaf Product members that have an Amount > 5 as well as a Count > 5.
    FILTER( {TM1FILTERBYLEVEL( {TM1SUBSETALL( [Product] )}, 0)}, [Test].([Posting Measures].[Amount]) > 5 ) ,
    FILTER( {TM1FILTERBYLEVEL( {TM1SUBSETALL( [Product] )}, 0)}, [Test].([Posting Measures].[Count]) > 5 )