Back in the day we were building a system to run on UNIVAC equipment but some brainiac decided that because we were a Bell System company, we had to use DataSpeed 40's (which buffered the screen and snap it up when the last character is received) instead of the UTS terminals on which the system was developed (which painted each character as it came in.
Users weeped and wailed to no effect that the change hurt them badly (which they could prove) because that while the two had the same time from first character to last, the operators could not start composing a reply when the first several lines had painted.