Giving up U.S. citizenship, or long-term permanent residence, is an immigration decision with a tax settlement attached. The settlement is the part people tend to discover late.
The exit tax
Expatriation can trigger a deemed sale of your worldwide assets on the day before you give up status, for anyone who meets the tests for a covered expatriate. Those tests look at net worth, at average tax liability over a period of years, and at whether your filings are up to date.
Being current is part of the process
Certifying several years of compliance is a step in expatriating, not an optional tidy-up afterwards. Someone who is behind may need to resolve that first, which is why this conversation and the Streamlined one so often happen together.
None of this argues for or against the decision itself. It argues for taking advice before the appointment at the consulate rather than after it.