I think this is mostly a revenue grab by the ACT. In the past, there has always been a hesitancy to retake because few schools officially superscored and the applicant was at risk that high subscores in one sitting may be lower in a subsequent sitting. Now this is better than superscoring for the SAT because you can truly just focus and study for selected sub components. Other than the $, there is little risk to take the ACT multiple times. I think it also skews comparative results because for better or worse, concentrating for 35-60 minutes vs close to 3 hours is a different test. It will be interesting to see if the College Board follows suit.
This change also on average probably benefits students who have access to better guidance on the application process even more because another gaming component is added. As far as schools admissions are concerned, it probably will have a mixed effect. This system will be advantageous to students who take advantage of this for schools that only look at 1 reported superscore. Less benefit for schools that ask for submission of all scores and already say that they look at each component.