[mistercow]

At the UI level, perceived time is usually more important than real time. Half a second with nothing happening feels long. A whole second with feedback in some form (a loading bar, a spinner, etc.) feels fast.

For longer wait times, this becomes critical. 5 seconds with no feedback feels incredibly, ridiculously long. 5 seconds with feedback feels like completely reasonable. I sometimes use almost entirely fake progress bars which asymptotically approach full when I have no way to measure how long something will take. It's bizarre, but even knowing that the progress bar is fake, watching it fill up makes the time seem shorter than staring at a spinner.

Actually improving loading time is important, of course, but the ROI is tiny compared to basic user feedback.