I record much less than I used to. I keep a spreadsheet for (rough) monthly income and expenses, but even that's probably superfluous. I used to do graphs and charts and collect a lot more data, but I think it was a writing avoidance mechanism. I used to track small newsletter ads' ROI before Bookbub started to like me, but once they did, the only data I need to know is "Bookbub works incredibly well and nothing else does," which even with my sieve-like memory I can manage to memorize that much.
Expenses all go through my business bank account. If I buy something for the biz, I use that credit card or Paypal or petty cash (though I've been on the same $100 of petty cash for six years). That way, at tax time, I just go into my bank account, sort to see only debits, export that as a spreadsheet, and plug the numbers in on my tax form.
What probably was more useful was tracking productivity. It kept me on track to see the "words written" slot being filled in every day, and if I tracked my mood or location or so on, I could see how external factors might change my word count or words/hour count. And I learned how many hours it takes for me to write a book, which is much fewer than I would have guessed before I began to track. (assuming I get down to work and don't fiddle about chatting on forums or whatever. ;) )