Not so sure. I do skim sometimes, but it always leaves me with are dirty feeling of cheating. Also one needs to go back and check whether something important was missed and this undoes most of the benefit of skimming.
The proper place or skimming would be to skim before reading just to get an overview of what's to come, or to skim while evaluating if the thing is worth reading in the first place.
The only reason I've ever had not to skim was because I was asked not to. But for example at school my purpose is really to learn not to satisfy the desires of my teachers, and actually most of the time reading, taking notes, and so on doesnt help me at all. Its a much smarter and more effective strategy. Trim the fat as the great adam levine would say.
