Andy Yun is speaking my language:
One thing that’s always driven me crazy is when I have large numbers in my resultsets and the lack of commas for readability. For a lot of different things I do, the more commas a number has, the more attention I want to give to a given value.
Andy shows examples of formatting to two and zero spots after the decimal, respectively. In a talk I give on analyzing business data with T-SQL, I also demonstrate how to show currency-based results:
FORMAT(SUM(o.Quantity * sih.LastCostPrice), N'$0,###.##') AS TotalCost
This starts each cost record with a dollar sign, ensures you have commas in the thousands spots, and have a two-digit decimal value. That would return back a result like $31,409,113.00, which is a lot easier to read than 31409113.