Not so long ago...
...I was given a task to convert an Excel Work Book into a web application.
The workbook was over 80MB. 20 of the tabs were for departments. There were 365 columns for figures for each day of the financial year + description columns with over 200 rows full of figures, budget data and formulas linking to other departmental tabs and hidden tabs containing look ups and other external files.
Multiple people used the workbook. It took ages to load, stored on a network shared drive.
The owners had to create a new workbook for each financial year. You can imagine with all those formulas, they bound to have a few pointing to the wrong worksheets/cells especially when they add a new department.