The problem with loading bars is that they lie. They promise a linear view of a 0-100% process that does not proceed linearly. Instead, they sputter and freeze, and most frustratingly often seem to get stuck at around 95%. Believe me, telling your user that the page is 95% loaded and then freezing for several more seconds is much more infuriating than a simple spinner.
This behavior goes way back to software like Real Player (buffering...), Windows Installer (which would actually hit 100% and then reset to zero for another round), and is seen today on YouTube, Netflix, and the browser's own feedback bar.
Can you predict the next few seconds of network bandwidth? Do you know the relative times of content downloading versus parsing json and browser rendering for various clients? All these play into the feedback you're promising, and you don't really know.
This behavior goes way back to software like Real Player (buffering...), Windows Installer (which would actually hit 100% and then reset to zero for another round), and is seen today on YouTube, Netflix, and the browser's own feedback bar.
Can you predict the next few seconds of network bandwidth? Do you know the relative times of content downloading versus parsing json and browser rendering for various clients? All these play into the feedback you're promising, and you don't really know.