I was forced to do this as a developer of Flash websites in the early 00's.

I loved making custom progress bars really fun so people didn't mind watching the huge sites download.

I HATED when they had me mess with the time so that it got to 90% really fast and then spent AGES finishing the last 10%.

We all know the Microsoft progress bars reached 99% easily and had an infinite last % in the '90s. I'm still not convinced that was by accident.