I think we are talking about the straight table object, is that right? I see three expressions where expression 1 and expression 2 are giving the same result, but expression 3 is giving a totally different output. If you are looking to get the sum of sales for the max category, then only your expression 3 seems to be working correctly here. But, you can improve this by changing your variable from Year(Max(Date)) to Max(Year). Other than that, I don't think there is much different between using a variable in set analysis on using it directly within the expression. I guess might be related how your team likes to use it and your personal preference.
