Aliases used to be this thing in the Mac OS, prior to Mac OS X, that allowed applications to remember where a file was located. More importantly, if you moved that file, the application could still find it. They worked across network volumes, too, automatically mounting a volume if necessary.
With Mac OS X, Apple recommends that an application store URLs to reference files. The problem with URLs is that they are just fancy pathnames to files, so if you move or rename a file, they break. To be fair, I've seen documentation that suggests CFURLRefs should be used only for transient storage of a file reference, but this gets abused across the board.
Safari's downloads window, for example, is guilty of this. Try donwloading something, moving it, and then finding it via the download window. You can't. And Apple puts the blame on the user by popping up a message saying, "Safari can’t show the file 'foo.pdf' in the Finder because it moved since you downloaded it."
Fuck you, Apple. So what if it moved? You can find it, almost always. You had tried and true, superior technology, and when you shitcanned or otherwise drove out all the true Macintosh engineers, replacing them with NeXT Unix weenies, you got rid of that good technology. Everyone knows engineers brought up on Unix are lazy, and don't give a rat's ass about the user. Well, that attitude shows through in Mac OS X.