What is the purpose of using VALUES or ALL in the first parameter of an iterator function?

Question

I know that only CALCULATE can modify the filter context. However following are 2 example using VALUES and ALL.

Example 1:

Revenue = SUMX( Sales, Sales[Order Quantity] * Sales[Unit Price] )

Revenue Avg Order =
AVERAGEX(
    VALUES('Sales Order'[Sales Order]),
    [Revenue]
)

What is the purpose of VALUES in AVERAGEX function? Is this to add an additional filter context?

Example 2:

Product Quantity Rank = RANKX( ALL('Product'[Product]), [Quantity] )

What is the purpose of using ALL in an iterator function?

Answer 1

Suppose we have a table like this:

ID	Sales Order	Order Quantity	UnitID	Unit Price
1	101	10	4	39.99
2	101	15	3	24.99
3	102	5	2	15.99
4	103	5	1	14.99
5	103	10	3	24.99

Since the Sales Order column has duplicates,

Revenue Avg Order = AVERAGEX ( VALUES ( Sales[Sales Order] ), [Revenue] )

gives a different result than

Revenue Avg ID = AVERAGEX ( Sales, [Revenue] )

since the first averages over the three Sales Order values whereas the second averages over the five ID rows.

Using DISTINCT instead of VALUES would work too.

---

Using ALL is instead of VALUES gives the same total but ignores the local filter context from the table visual:

Revenue Avg All  = AVERAGEX ( ALL ( Sales[Sales Order] ), [Revenue] )

In this context, ALL is acting as a table function that returns all of the distinct values of the column specified ignoring filter context.