Shared workbooks work the best when everyone is using Office 365 within the same organization, known as a “tenant” to those who maintain the Office 365 environment. While there might have been simple workbooks that could live within these limitations, the functionality was very limiting. You had to agree to avoid a long list of features that weren’t compatible with shared workbooks. It was clear that the old limitations of the legacy Shared Workbook experience weren’t practical in real life. The Excel team describes the new coauthoring experience as “Excel’s moon shot.” The team spent more than three years on the feature.