I've written before about the problems of skimming and scanning (e.g. here). Over the weekend I taught an IELTS course here in Manchester, and we found another problem with scanning. I'll try to explain below.
In one practice test passage, the first question contained a name, and we decided to scan for it. We quickly found the name in one of the later paragraphs in the passage, and so we jumped straight to that paragraph and found the answer. The problem came later. Because we hadn't read the passage from the beginning, we didn't really understand what the whole article was about, and we felt lost when doing some of the other questions. "Scanning made me panic" is how one of my students described it.
Scanning encourages you to 'jump around' the passage in a disjointed way. It might help you to find one answer, but it will probably make your life more difficult overall.
Sometimes "slower is faster". Get into the habit of reading the passage at normal speed from the beginning. Go through it question by question, and resist the urge to jump around.