Power Fx function

With — Power Fx function reference

Name temporary values inline.

Syntax

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With( { Name1: Value1, Name2: Value2, ... }, Formula )

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With({tax: 0.1}, total + total * tax)

→ Computed value

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With({subtotal: Sum(colCart, Qty * Price)}, subtotal + subtotal * 0.08)

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With({rec: LookUp(Staff, ID = locId)}, rec.Name & " – " & rec.Department)

With is a naming convenience scoped to the current formula only — the named values do not persist outside the call the way a Set()/UpdateContext variable would.
It avoids re-evaluating an expensive sub-expression (a LookUp, a Sum) multiple times in the same formula — without With you would otherwise repeat that sub-expression for each use.

From Table shaping