Fracture as a Cross Class:
Fracture does 220 potency of damage provided it ticks its full duration. Below level 60, this is a DPS increase over just spamming the Rage of Halone combo (which averages 203 potency across its 3 GCDs). However, once you get to 60 and get the Royal Authority Combo, Fracture becomes almost completely useless. Royal Authority combo has a 230 potency average, and Goring Blade combo has even higher. Therefore, Fracture is almost always a DPS loss to use. People will try and convince you that it's a DPS increase to use as the last move before Fight or Flight falls off, or as a filler so you don't clip Goring Blade's DoT... but it isnt. The math shows that in a straight fight where you're just tunnelling DPS onto a target, Fracture is always a DPS loss, and also a huge TP loss.
The one situation where Fracture can be a DPS increase is when you have to leave a target (as Khalithar says, like in Alex 1 where you're DPSing the main boss for a while and then have to go pick up the second). However it's ONLY a dps increase in this situation if you have to leave the target 1 gcd after you finish a combo. Eg, if you finish a Royal Authority, and have 1 second before you need to move, a Fracture would be better than doing a Fast Blade. But if you've already done a fast blade and need to move, doing a Riotblade would be better. Also, all ticks of Fracture have to do damage to make it worth ticking, so it doesnt work to throw it on the Alex Oppressors before they leap away as they go invulnerable. Also, if you are able to return to DPSing before your combo times out, a Fast Blade would have been better (eg, Fast Blade Oppressor 1, turn and run to Oppressor 0.5 and do a Riot -> Goring before it times out, would be higher overall DPS than Fracture on 1 and starting fresh with fast blade on the second).
All in all, the situations where Fracture result in a DPS increase are so horrendously small that I recommend not taking it - you'll be too inclined to press it -thinking- you'll get a DPS increase when in 95% of situations you'll end up doing less DPS AND nerfing your already starved TP. I now actually take Protect as my fifth cross class so I can speed up buffing before a pull, help buff ressed people to save healer mana in awkward situations, and keep myself buffed when soloing or working in small groups without a healer - though this is just as niche as taking Fracture really, so you might just want to keep Fracture on your bars for doing downsynched 50 content.