I keep forgetting how to do this. Perhaps posting it here will help.
There's a simple syntax for referencing data in other sheets. Enter the name of the sheet followed by an exclamation mark before your formula.
In this example, the result would be cell B22 from the "Marketing" sheet. If the value of that cell changes on the Marketing sheet, it would change on this sheet as well.
This makes things like my make\break event budgets easier to build and review. I like being able to segment the numbers into buckets that match the way I'm thinking about the project plan.