Challenge modes have been in the game for some time now, but patch 5.4 added another type of content where gear is scaled down, and that's proving grounds. Proving grounds, unlike challenge modes, are already being used to gauge the quality of players, with groups asking for certain ranks or achievements in order to join them. So how best do you arm yourself for this content? Gear scaling is certainly one hurdle to overcome, and it's a tricky one, as it's not easy for the average player to work out just how their stats are going to be scaled with the reduction to ilvl 463. And you can't always carry every potentially viable piece of gear with you to the Temple of the White Tiger to see what works.
And that's where Wowhead's gear scaling checkbox comes into play. While it's far from perfect, it's certainly helpful. As you can see above, we're looking at a tank trinket
that drops off Garrosh. It's not ilvl 463. In fact it's ilvl 553, in this example at least, but by checking the "Challenge Mode" box, it's downscaled to 463, as it would be in-game. You can see what works, what the numbers will be, what the procs will look like and so on. Go forth and prove yourself!