I can see the reason clearly the 'for' - ie: those with 20/20 vision can cleanly see what is being used easier, since only those options ticked are clearly visible.
However as orioncrack points out it doesn't help all - especially when there's the attempt to adopt the Accessibility - W3C for both websites and their apps.
Here in Aus the gov has a mandatory requirement http://webguide.gov.au/accessibility-usability/accessibility/ to meet WCAG2 as also noted here Web Accessibility Initiative (WAI) - home page.
Perhaps a slightly bolder font for those being used? Or even a per user option to hide all not used (ie don't load the list of all) maybe the way to go.