Often, I don’t. If I think there is a good chance of a payoff, though… I start skimming the crap. I’ve learned to skim through stuff until something of import comes up, and then I step back a couple paragraphs and start reading again.

I don’t know how you’d learn this, but I learned it back in high school when I needed to find information in the textbook quickly, but couldn’t afford to actually read every page on the way. It was massively successful back then, and now both.

If after skimming like 1/4 of a book I haven’t found anything interesting again, I almost always quit, though. It’s really unlikely that a book with that much content that I don’t care about will have anything that I value later.

That said… I have skimmed entire books on re-read. Some of the middle Wheel of Time books, for example. And some were so bad that I just read a summary, instead of skimming. But I like the first books enough that it was worth it for the ending, which was decent, but not mind-blowing like I’d hoped. (I “re-read” them when the later books finally came out and I wanted a refresher.)