I do in fact use an external unit, but only because the internal units on every Mac I have owned have failed due to Apple using very low quality, poorly designed Chinese sourced hardware components. This same low quality internal "SuperDrive" unit is in the add on Apple external optical disc.

The external third unit is pretty noisy, has a large wall wart, and takes up desk space which contributes two cables, power and USB, as well as taking up one of the small number of USB ports on the Mac. This is an exceptionally poor design compared to the experience of using a PC which reasonable comes with an optical drive, something that I use very frequently, as do most computer users.