* ledger is for double-entry accounting. Doing that in a spreadsheet can be a huge pain. When you then want to query the data in different ways, that will add a ton of complexity to your spreadsheet.

* It is plain text, so you can keep your data in version control.

* It has awesome reporting capabilities. These are builtin, so you don't have to create them from scratch.

Spreadsheets are nice and simple, but once you do anything moderately complex you are asking for bugs under all of your hidden formulas.