I don't use it either, and I agree with the poster on that stackexchange link about it sounding like manager/marketing-speak, but when I see it, it makes me pause for a second to think about what really means (perhaps that's the point) --- I had this exchange with a coworker not long ago:
CW: ...and this way it'll be more performant too.
Me: Performant? As in faster?
CW: Yes.
Me (to self): Then why didn't you just say it'll be faster?
IMHO it obfuscates meaning and should be avoided; the surrounding discussion/vagueness about what it means (I don't think it means efficient, but only faster --- as in, a high-performance car) shows that too.