It has a couple of advantages:
Rendering begins sooner. The browser cannot layout elements it hasn't received yet. This avoids the "blank white screen" problem.
Defers connection limits. Usually your browser won't try to make more than a couple of connections to the same server at a time. If you have a whole queue of scripts waiting to be downloaded from a slow server, it can really wreck the user experience as your page appears to grind to a halt.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
