You have to ask yourself what you're going to do with the data. Don't just collect data for data's sake.

The most granular I've ever needed is things like: "wow, I've spent way too much on hobbies in the past 3 months" or "we've spent way too much eating out this month" or "the kid's sports are getting out of hand". Or even "we can afford to spend a lot more on vacations over the rest of the year".

Those are all very top level categories. I can't imagine a world where I'd ever make a lifestyle change based on how I spend on meat over the past six months.

And if you're not actually making a change then the data is just data hoarding.