SMB Validation

What is an appropriate audit trail for an Excel Spreadsheet? Some indicate you should track every single cell change and others say it should be tracked the same way a document management system would do it (track final versions only, intermediate drafts don't count only after all changes have been made and approved)?

The audit trail for Excel should capture changes to both the data and to formulas. Things like formatting changes (alignment/font) to cells do not have to be audit trailed.