‘Some of them are less readable than the individual letters’
Daniel Will-Harris on ligatures:
While ligatures do add a subtle finishing touch for some classic typefaces, and specially designed ligatures […] are beautiful, they are not essential in most cases. In some cases they actually make type more difficult to read.
The real point is for you to look at the faces you’re using and see if they really need ligatures, or if, in fact, they are actually getting in the way of readability for the sake of “aesthetic” (which is in the eye of the beholder) fineness.