It's something I've noticed about you that I find a bit irritating at times.
It doesn't totally enrage me or keep me up at nights, it's merely an observation.
I don't know why you would write in a way which is harder for people to understand and makes your posts less clear.
It was fairly obvious what "efficacious" means, but if there is a difference between it and "effective" then it's a pretty technical one which most people wouldn't know - as I said, Lily the Pink is the only other use of it I've encountered, and I suspect The Scaffold mostly used it to be silly and because it scanned. Where's the "cost" in using the word "effective"? It's a clearer word, it makes your post easier to understand and it's even 2 letters shorter - a whole 18% saving! Most people modify the way they talk for different audiences in the interests of being understood.
Language is about communication. When people say "6 items or less" I do enjoy muttering "fewer!" under my breath. I had the pleasure of correcting an English teacher about that at the weekend. But, actually, I don't really care about that one. I do it because it amuses me. While I'm a bit of a Grammar Nazi I mostly care about clarity. If someone says "6 items or less" the meaning is perfectly clear.
Your incentive is clarity and being understood.