Is 5.6ms really significant? You should be typing like 200 characters
per _second_ to really notice the difference.
Even 12ms that I'm getting at the bottom of your example file doesn't
sound like it should have effect on the perceptible latency.
That’s a totally fair question, but yes, I can feel the difference while typing. Ever since switching to Emacs I could feel significant latency in my setup so I’ve been on a quest to bring it down. That quest led me to smartparens and first to that case-fold-search binding issue and now here.
Even if one can’t feel 5.6ms, it becomes another brick in the bag, i.e. if another minor mode did something similar and added another 5.6ms. With enough of them most people could probably feel it.
If you haven’t read it, I recommend looking over https://pavelfatin.com/typing-with-pleasure/
He has a tool on there for measuring typing latency. Here is a histogram of the difference between typing at the bottom of the sample file, the top, and the bottom with memoizing syntax-ppss in smartparens:
