Depends how intricate your taxes are. Perhaps 30 million people file Schedule C, which covers freelance income, gig income, etc.

The IRS will (mostly) know your gross income, but it won't know the exact details about claimable deductions such as business travel, business meals, supplies, etc.

The only way it could know that would be to peer inside your credit-card statements, bank statements, etc. and make judgments about what was work related and what wasn't.

I'd rather do the tallying myself -- which is a chore -- rather than have IRS software make guesses that are a) awfully nosy and b) bound to disadvantage me.