The non-submitting student has to be stronger in other aspects than their counterpart who has an impressive score in their pocket.

This past year, 47 colleges and universities announced that they would adopt “test-optional” admissions, meaning students can be considered for admission without submitting an SAT or ACT score. Nationwide, there are 850 such schools according to the National Center for Fair and Open Testing.
Why are colleges going test-optional?
The goal of these colleges is simple: to broaden their application pools. With larger pools of students to choose from, they can be more selective. If they appear to be more selective, they can possibly move up US News and World Report’s annual rankings.
For the student, the implications are a little more complicated. First, these schools tend to be smaller liberal arts colleges. Fewer large universities have joined the test-optional ranks. If your child has big dreams at a big school, skipping the test is probably not an option yet. For competitive prospective majors, such as pre-med or engineering, non-submittal is usually not an option altogether.
Which students should consider not submitting a score?
Of course, the prospective student who chooses not to submit a score fits an obvious profile: they are strong overall but have underperformed during the testing process (or have avoided it altogether).
The non-submitting student has to be stronger in other aspects than their counterpart who has an impressive score in their pocket. Test-optional schools tend to have more strict cutoffs in other areas, particularly GPA and class rank. According to the New York Times, one school (George Mason University) will not consider a non-submitter with lower than a 3.5 GPA and a top-20 percent class rank. AP scores, International Baccalaureate participation, and extracurriculars play a bigger part.
So, if your child is exceptional in everything but their test scores, not submitting might be an option (although working toward an exceptional score might open up new college opportunities).
If your child is borderline all around, they still need to strive toward an impressive SAT or ACT score. It can make a big difference, no matter which school they are trying to attend.
Does the increase in test-optional schools signify the death of standardized testing? Probably not. Both tests are spending a lot of time, money, and effort revamping themselves to increase their relevance to the colleges. What colleges are always trying to see throughout the process, with the help of all the evidence, is a picture of the kind of student your child will be.