Sometimes you can't get everything you want from just three colors. Sultai Control is certainly serviceable in the new Standard format, but what if you needed something else? Maybe there's a card that is so versatile and so important to your gameplan that you end up splashing it.
Temur Charm might be that card.
DICH4690 went undefeated in a recent Daily Event on Magic Online by splashing Temur Charm. It's a situational removal spell, a situational counterspell, and a situational win condition, but that's the beauty of the Charm cycle. No matter the situation, they should be useful to have.
In this case, we have four copies of Hornet's Nest that are aching to fight something, and Temur Charm provides that while also giving you a little more insurance against big spells that can get Mana Leaked. By using Temur Charm instead of something like Savage Punch, you gain a way for Hornet's Nest to profitably fight 2/2s and live to fight again, whereas Savage Punch is useless without a creature and is difficult to turn on the ferocious side of it.
A horde of hornets is going to be difficult for any deck to break through and even provides you with a way to pressure planeswalkers. Overall, I think Hornet's Nest is being undervalued right now. Sometimes you have to go through some trouble to push it to its full potential, but I think this deck does that quite well.