I think those benefits are quite similar to having more programs failing to run (due to static and strong typing, other static analysis, and/or elimination of undefined behavior, for instance), or more data failing to be read (due to integrity checks and simply strict parsing): as a user, you get documents closer to valid ones (at least in the rough format), if anything at all, and additionally that discourages developers from shipping a mess. Then parsers (not just those in viewers, but anything that does processing) have a better chance to read and interpret those documents consistently, so even more things work predictably.