If like me you’re traveling often, and develop while doing so, you don’t want to waste time. Every laptop nowadays has a wifi interface: problem is finding the hotspot, not an easy task on a plane or on a train. Once, I used to download and save each and every Javadoc of Java, JEE and the various OpenSource frameworks I used (Struts, Hibernate, Spring, you get the idea). As bad luck would have it, 9 times out of 10, I hadn’t the correct version when I needed it.