Fetchlands - Admittedly, I'm very anti-"fetchless" storm. The benefits of "fetchless" is that you're able to dig deeper and not see cards you may have scried to the bottom. This is a doubled edged sword, especially if you're running Empty the Warrens. Putting Grapeshot, Empty the Warrens, or Repeal on the bottom means that card might as well be exiled the rest of the game if you ever need to find it again.
I've heard the "You take less damage because of not having fetchlands" argument, which I believe is blatantly false due to not running four copies of Steam Vents and Shivan Reef.
With running fetchlands, you're protected from things like Blood Moon and in fact, you can even play it yourself. I was running Blood Moon up until my testing for this event when I determined it's not good in the metagame. Another benefit is that you're giving away less information, twice at GP Hartford my opponent confused me for Blue Moon which ended up being favorable.
While marginal (much like the scrying from "fetchless"), you thin your deck and are less likely to flood out in the course of a game.
Snow-Lands - They aren't needed if you run fetchlands since you can always just search up four different lands. Also, playing these gives away too much information right off the bat. I've searched up lands once in my experience with the deck and it was only to thin my deck while looking for a bounce spell. The downside of telling your opponent what you're playing is way worse than the tiny possibility that you need two copies of Island with different names.
Empty the Warrens - The main deck copy of Empty the Warrens is multi-purpose. It happens to be terrific against decks like Jund, Grixis Death Shadow, BR Hollowed One as well as providing depth against the format. By that, I mean that it provides you with alternative ways to answer things like game one Leyline of Sanctity, Meddling Mage, Graveyard Hate, Runed Halo, and other anomalies.
Defense Grid - These were the Blood Moon slots, I felt like my control match-up needed a slightly boost and this card is a heavy hitter. Alternatively, it could be something like Gigadrowse. My concerns with Gigadrowse are that it's very slow and forces you to need a lot of lands in order to beat control decks. I don't want to be cantripping into lands in order to make my protection spells work.
That said, this slot was rarely used in the GP except for the lone control deck I faced. They could be something else as the metagame is very fast and aggro based at the moment, but I'm not sure what it would become.
Pyroclasm - I wanted an extra card for humans and in my testing, Anger of the Gods was too slow because of Thalia, Guardian of Thraben. Throughout the course of the event, I also experienced the sweet, sweet bonus of Baral, Chief of Compliance living though Pyroclasm I was initially concerned with it because of Thalia's Lieutenant, but it never came up in my testing or at the event.