I do that a lot, especially when I want to finish a book fast.
What I would do is skip lines when I read and I finish up the sentences in my mind. Hence, I never really get a complete picture on what is going, just the main plot.
If I like the story, I would re-read it, and usually, I don't brisk read the second time. Even if I do, the lines I did not read previously, I tend to read it then. So... the entire picture is ultimately formed with the missing puzzle pieces I've discovered during the second read.
But, of course, there are times that I don't brisk read. And when I don't brisk read, I take a long time to finish a book. This is not because I'm a slow reader, but because I'm easily distracted. I have a computer and I have internet access, and if I take my own sweet time to read and devour a book, I end up not finishing it, UNLESS, it is really interesting, like Harry potter, or Hunger Games.
Anyways, I'm currently reading Pastworld. I'm almost halfway into the book, and I started reading like 2 hours ago? It's a pretty interesting book, but it's those kind of books that if I put down, I'll put it on a long hold, just like The Child Thief, which I have stopped reading all together.
Hopefully, that won't be the case for Pastworld.
I now leave you with a lame book trailer of Pastworld. I assure you, my imagination is way better than the trailer. In fact, don't even watch the trailer... it does no justice to the book. Don't even click on it.. it's a waste of your time.