The advent of the dual spec system has made it possible to retain a buff after switching. One such instance of this is allowing you to use the hunger for blood self buff, and switch to a spec that doesnt have the talent. HFB got buffed to a 1 minute so you still get a good amount of uptime after switching specs.
So basically:
-fight a mob, get it under the effect of a bleed, and use hfb when it is about to die (so that you are out of combat right away)
-switch to your alternate spec, this takes 5 seconds
-enjoy hfb for a good 50+ seconds while using the skills of the other spec
Clearly this is very situational, but a 15-18% damage bonus is nice. This could be used when soloing, and you are about to engage either a tougher mob, or a pack of mobs, and wish to have the hfb buff along with KS/AR/BF/FoK. Even in a raid situation, it would be a big bump in your numbers if you anticipate a large aoe pull and have this ready to go.
This technique can be applied to other classes as well i'm sure, so long as its a self buff with a decent length of time on it. Also, this is clearly not an intended mechanism, changing specs drops people to 0 mana, so it would be assumed that it would drop your talent-specific buffs as well.
Proof:
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