A long last, Excel is getting a quick summary of the workbook statistics including the bounds of the sheet, tables, formulas and external connections.
Look on Review | Proofing | Workbook Statistics in Excel 365 for Windows or Mac.
There are details for the currently selected sheet and the whole workbook.
It’s similar to the Word’s long-standing Word Count feature also at Review | Proofing.
Workbook Statistics are now in Excel 365 for Windows, Slow insiders (Monthly Channel (Targeted) v 2004, build 12730.20150 and later. It’s also in Excel 365 for Mac, Insiders releases.