True, but back then there was no "CPU power saving" mode. The CPU was slow and it always run at full speed (power was cheap back then).

In the Windows NT series (4, 2000, XP, etc.) the sheduler gives the forground application an higher priority. It runs a longer CPU time than all other applications. This was probably also similar with Win 3 and 9x series but probably with many hacks and glue code on top of DOS.

Moving the mouse also prevented the screensaver, an application that would "save" the screen by drawing fancy graphics to prevent static phosphore burns on CRT monitor and slowed down the system