On Mac Mini Server
Screen sharing on a Mac Mini Server that has no display attached (headless) is
low-resolution and
slow.
On a headless PC
One of the key requirements in using a PC without a display attached (headless PC) is remote desktop access, but in many cases configuring the headless PC to support high resolution remote desktop proves to be so challenging that sometimes users connect a display to the PC just to be able to have remote desktop access!