User blog comment:LivesByProxy/Vision: Sight, Stealth, Detection, & Denial in LoL/@comment-24464243-20151015101734

What you call "x-ray vision" is pretty much just flying vision from RTSes and other MOBAs.

It's, uh, pretty ridiculous for win-moring in said other MOBAs. Granted, most of it is actually centered around abilities like in League, but in DOTA specifically there's two characters that can purchases flying vision during day and night, respectively. Get one on your team and you're at a massive advantage during half the remaining match. Get both and non-stealth means of approach are effectively meaningless. Get both and plop some true sight on one? Hey, now not only is the stealth option gone, but the enemy team is unlikely to have any wards now, period!

Granted, these are pretty extreme examples locked behind a 4200 gold payment for purely utility purposes and some decent tank stats, but being able to see everything within a certain range, regardless of terrain, is a pretty big deal. Heck, similar reasons are the main limiting factor for Rek'sai, considering how much of a deal she is in pro play. It's definitely something that would need to have eyes pointed at, and might actually cripple the champion it's on simply due to its power.