i'm pretty surprised your professor encouraged you to skim... in my foundations of nursing course, we didn't have exams or quiz's, but we did have many papers to write. we were required to do all the reading, and our professor always emphasized the importance of completely understanding the material in the course. having said that, i'm an extremely lazy person, so i always skimmed through the pages. made it out of the course with an a : )
i don't feel like i missed out on anything. skimming isn't skipping. if you're going to skim, then i suggest you read the first few lines of each passage, if you understand it, then skim the next page of "explanations". if you don't understand it at all so far, you probably shouldn't skim.