>The challenge is that you personally need to report additional information for things like capital gains tax on asset sales, any credits/deductions you wish to

>The challenge is that you personally need to report additional information for things like capital gains tax on asset sales, any credits/deductions you wish to claim, and changes in your living arrangements or life status. But that's exactly what the parent comment was saying: you'd get a notice from the IRS that says they think you owe $X based on their records. You have until the filing deadline to file any additional income/exemptions/deductions/challenges/etc. As you say, for the vast majority of people this would make taxes a million times easier. For people with more complex situations, they can then engage in the more complex process of additional filings.