Lazy Loading Assets (opens in new tab)

if your user goes to your site twice, he has your assets in cache.

Because you're making dubious gains saving a couple KB of bandwidth by sacrificing the responsiveness of your app when you introduce an additional round trip for each new piece of code. It may look fine for you, but there are plenty of people that don't have super-low latency, high bandwidth internet connections.

optimizing for cache hits and only loading the code for the view you need are not mutually exclusive. Your build can package optimized assets at a page or component granularity. But parsing a little bit too much javascript is not so slow as extra requests, doubly so considering that the biggest unoptimized assets are the dependencies that every page needs, like jquery, angular or whatever. I have worked on several gmail-sized apps and, to date, the profiler told me not to bother.