Exactly as the title says: what is the role of expense tracking in the long term?

I can understand expense tracking being very beneficial in the short term if you've recently changed your lifestyle or are going through any sort of financial difficulties, but what about after this has passed? What is there to be gained by painstakingly tracking all your expenses year after year even when you're doing well financially? Obviously tracking expenses takes a non-negligible amount of time, so I'm wondering what you get out of it. Would the long-term data and reports you'd get from doing this be worth the time and effort it takes to enter in the receipts, reconcile accounts, etc.?

(I understand there are sites like Mint.com which can remove a lot of the work, but in the interest of privacy, I prefer to offline tools like GnuCash).