There's also the case where the spreadsheet contains a whole bunch of endlessly duplicated and error-prone cell logic that nobody really understands, partly designed to work around limitations in the underlying cell-programming model.
When you say "shared" do you mean the Excel file is kept on some network drive and that multiple people can access it there?
- one spreadsheet is shared among more than about 5 people (or they each have their own version of it... shudder)
- the sheet has more than about 10,000 rows
That's the point where Excel truly starts to be not the right answer.