Comment by floodle

It's about the value to you versus the effort you put in. For me the granularity you are talking about is too much effort. All my supermarket shops go in one big category "groceries and household".

Start easy and see what you want to get out of the data. If you can store the original source (e.g receipts) so that you can later go back and increase the granularity if you find yourself wanting it, that would be ideal.