Once you pushed an app beyond the level of usage the developer had performed in their initial tests, it would crawl to a near-halt, thrashing the disk like crazy on any save. Apple's algorithm would shift huge chunks of the file multiple times per set of updates, when usually it would be better to just rewrite the entire file once. IIRC, part of the problem was an implicit commitment to never strictly requiring more than a few KBs of available disk space.
In a sense, the resource fork was just too easy and accessible. In the long run, Mac users ended up suffering from it more than they benefited. When Apple finally got rid of it, the rejoice was pretty much universal. There was none of the nostalgia that usually accompanies disappearing Apple techs, especially the ones that get removed outright instead of upgraded (though one could argue that's what plists, XML and bundles did.)
