Create checks such as isblank() or iserror() so that I can dictate what happens when an error occurs.
Example of the problem I run in to: I have a "Save to Parent" formula that counts the child records of two different types. I then have a "Save to Record" formula that subtracts two fields on the parent record. If the "Save to Parent" formulas haven't run yet then I have blank fields, and since these formulas occur on different entities I can't use the execution level to control which runs first.