One thing that really annoyed me in some monospaced fonts with ligatures is the [] ligature, I never understood why would someone rather see a box instead of two brackets. I'm no typographer, but I think that it makes the text lose its uniformity, because [] and [0] will look weird close to each other.

I guess I'm not alone in this, because in the Fira Code repo there's this commit from 2 months ago: "Remove [] ligature from specimen".