There would be questions 4x per year instead of once per year, at least for tax preparers...
As much as I do not like how employees try to blame employers for incorrect WH (which trickles to me, for which I have to say the employer, via our software, withheld exactly what the employee directed via their W4) - if the process was easy enough to remove most questions, there would be nothing for me (us?) to process at all. Kind of like how modern consumer vehicles have become reliable enough there is much less need for skilled mechanics (just people who can replace what a computer tells them to replace).
While I do not spend time digging into the issue, I have to wonder if those who were opposed to a very similar change for 2019 were worried about how the new form will actually be easier, versus claiming it will be harder. From my personal perspective (payroll) it is absolutely little effort to program, and the form itself reads easier than the old form, for those who traditionally have had issues getting close to even at the end of year. Of course, change is good for me/us, and when eventually there is a new administration in charge, there will be change again since net pay and appearing to give more has been an issue for every administration going back for quite some time.