This can become a deep math equation before it proves itself to everyone, so I'll try to start low.

If we use WAR's Butcher's Block Combo, their highest potency combo, as a base, we get an average potency of 216.67 = [(150 + 200 + 300)/3].

I don't even think anyone is arguing the opener, but if people want to, I can go further after this. That said, if we look after the opener and, imho, give a generous estimate of two combos per Fell Cleave, the new average per GCD becomes 257.14. Fell Cleave basically adds an extra 50 potency average to each GCD, amazing right?

Fracture is 300 potency is allowed to tick, so the benefit seen spread out is not going to be as high as Fell Cleave, but it's still an extra GCD of higher potency than each average GCD in this scenario. That alone justifies it.

To further drive this point, if we received a Fell Cleave after every single combo, the average potency would be 287.5, which would mean Fracture is still a DPS bonus.

Things that make no difference in this:

• Using Storm's Eye. We assume that Storm's Eye is kept up for the full rotation. Always get Storm's Eye up before anything else and keep it up. Never let it drop. If you're off the boss and it falls, Storm's Eye should be the very first thing you put on the boss. The only time I've seen where Fracture can arguably be put on before anything is in the beginning of the WAR opener where you can possibly get an entire Fracture up before applying it during the Berserk window. This will take more math to clarify, but I can do it if you wish.
• Maim. This takes care of itself if you're keeping up Storm's Eye, but it's even more important than Storm's Eye for WAR DPS.
• Infuriate. This is essentially a free Fell Cleave/Inner Beast and doesn't affect the math of averaging out the rest of WAR's rotation.
• Berserk. This merely makes every attack within that window stronger, so you want to prioritize your strongest attacks. Hence why we do the triple Fell Cleave opener in the first place. If Storm's Eye is going to fall off because you applied Fracture, you need to sort out the order of your Berserk window.

To conclude: Use Storm's Eye first, keep Fracture up unless it isn't going to tick all the way (e.g. the end of a fight), and if you are losing Eye at some point you've messed up somewhere so you should fix that because your DPS is not optimal anyways. Always remember that Eye is not just buffing your DPS, so that alone should stress the importance of keeping this applied. If you have to sacrifice Fracture for Fell Cleave in your opener's Berserk window, you've either made a mistake or you ridiculously low skill speed and are saving CDs. I personally don't play WAR enough anymore to tell you every instance this actually might occur, but we're talking about pure DPS here anyways.

"Optimal DPS" involves keeping Fracture up 100% unless you will not receive the full duration.