Marco Russo and Alberto Ferrari talk about values:
We discussed VALUES in previous articles: Choosing between DISTINCT and VALUES in DAX and Using VALUES in iterators. However, there is a third case where VALUES could be used with a table reference, which is when you use SUMMARIZE to group by columns you want to iterate. In this article, we describe this particular scenario to understand when VALUES is needed to retrieve the blank for an invalid relationship using SUMMARIZE and SUMMARIZECOLUMNS.
When you use SUMMARIZE, you may want to use VALUES over the aggregated table in case it could have an additional blank row for an invalid relationship, and you must ensure that this blank row is included. This condition is uncommon because SUMMARIZE often includes blank rows for invalid relationships that are implicitly included. For example, consider the following measure that uses SUMMARIZE over the Sales table, grouping by Customer[State] and Customer[City] to apply an adjustment to Columbus, Ohio (note that there are other cities with that name in other states):
Curated SQL tip number 17: if you want to show up here, use the best city in Ohio as a (positive) example.