Why do some decks run Sword of Fire and Ice in main?

[Megadeus]

Plus just naturally drawing a weapon that your opponent hasn't prepared for (like a SoFaI off the top) is pretty devastating

[Bed Decks Palyer]

I loved to play Faerie Stompy with the 3/3 or 3/2 SOFI/Jitte split. But at the end I turned to 2/2/2 SOFI/SOLS/Jitte, as it gave me pro:Swords in case CotV didn't stick, moreover the CA gained by both the raw draw of SOFI and recuring Mulldrifters via SOLS was amazing... and much needed in a deck with sets of Chrome Mox, City of Traitors and FoW.

That was one of my most beloved decks and I should not have sold it. Frankly, I don't think that it's any good in a world of Delver, Abrupt Decay and Wastelands everywhere... But I still should have kept it for nostalgic value.

[Zupponn]

I ran both a single Jitte and a single SoFI in my Dragon Stompy deck that top 16ed an SCG Open. I had no way to tutor for either card, but I never wanted to draw 2 Jittes, so I added the next best thing, which was the Sword. My deck could have easily ran a Batterskull, but the utility provided by the Sword was far more powerful than a simple 4/4 lifelinker. Protection from red and blue seems so undervalued by many people.

[Ellomdian]

How do people justify playing SOFAI?

Because it's debatable whether it's the best piece of equipment in a vacuum? Jitte requires counters to be good, Batterskull is hard to cast unless you're cheating it into play, and SoFI has an immediate impact on whatever it's equipping that's relevant in the format and it has a really good ability when it connects, which said ability allows it to do reliably.

If you are playing SFM and only have room for 2 pieces of equipment, it typically makes sense to run Batterskull and Jitte to polarize the effects - in any given situation, one of them is likely to be clearly better than another. If you have room to run 3, SoFI becomes the 'best' equipment in abstract, because it doesn't suffer from the 'flaws' of the other 2.

[Wilkin]

I think its wroth! I mean its not like you play a playset; Ill just devote 1 slot to make my toolbox better -> skull/jitte/sofi seems like a solid package!

Also its super akward if you run 4 sfm and just 2 equipments...

I hear ya. I used to run 4 mystics and 3 equipment main and since I don't run Brainstorm (or blue for that matter), I would sometimes have nothing to search for. I'm at 3 and 3 and it's been great.

As far as question is concerned. The abilities on SOFI if you connect is insane and IMHO the best overall of all the Sword of X+Y. Hard to beat Shock and Draw. Sometimes with the other swords the abilities aren't as relevant. 3 life may not matter if against combo, might not have a creature in the yard to return, untapping lands for a non-blue deck is kinda meh etc.

[HdH_Cthulhu]

Yeah its still bad if you clutter your hand with too much weapons (especially vs mana denial), but at least your sfm dont turn into squires xD

[YamiJoey]

Batterskull, generally, is way better than Sofi against Miracles. The only time that's not true is when you have a TNN. We kill threats really easily, so keeping the Sword on something isn't easy. Batterkull is difficult to counterbalance, and provides you with a threat. If you can make it, bounce it, and cast it again, you are going to gain a significant advantage. You just 2-1'd us, if not better if we have to Force it on the way down. That's how you beat Miracles with decks like Jeskai Stoneblade, not by making a guy and turning it sideways as fast as possible.

I have only rarely opted for a main deck Sword, but I have played Faf, Wap, and Sofi all to great effect when the format is right for them. If everyone is on BUG Delver, I would play Faf in an instant. If RUG Delver was popular, Sofi and Wap are both really good. If Jeskai is popular, the Sofi is basically the game. I think Jeskai might want Sofi as an edge in the mirror. You can make basically anything against most of the field and the random value, or huge swing in clock will get you there, but having the Sword that beats you in the mirror is marginally better than having one that is just really good. As for DnT, I imagine Wap is unbeatable, and Las is probably even better. (Buying back the things you traded off early seems brutal.)

EDIT: Also, a TNN with Sofi is a 2-3 turn clock, whereas it's a 3-4 thrn clock with most of the other onces. The advantage over Wap of drawing cards instead of gaining life is obvious.