This is a special post for quick takes by David Udell. Only they can create top-level comments. Comments here also appear on the Quick Takes page and All Posts page.
You can usually save a lot of time by skimming texts or just reading pieces of them. But reading a work all the way through uniquely lets you make negative existential claims about its content: only now can you authoritatively say that the work never mentions something.
If you allow the assumption that your mental model of what was said matches what was said, then you don't necessarily need to read all the way through to authoritatively say that the work never mentionssomething, merely enough that you have confidence in your model.
If you don't allow the assumption that your mental model of what was said matches what was said, then reading all the way through is insufficient to authoritatively say that the work never mentionssomething.
(There is a third option here: that your mental model suddenly becomes much better when you finish reading the last word of an argument.)