A family of Microsoft spreadsheet software with tools for analyzing, charting, and communicating data.
Note that I wasn't being authoritative when I said this might make the sheet resource-hungry; however MS themselves state "Formatting cells on your worksheet can make the right information easy to see at a glance, but formatting cells that aren't being used (especially entire rows and columns) can cause your workbook's file size to grow quickly."
You don't have to believe everything the seller promises. .-)
IMHO, if this really were a problem, we would be getting threads here almost every day reporting massive performance losses.
But of course there are individual cases where some users manage to do it. And if they don't have professionals like us to ask, then they need an add-in that solves the problem ... maybe.
Andreas.