High-resolution monitors
To be useful, a computer must produce output in a way that makes sense to the user. Of all the computer parts capable of interfacing with the user, monitors are the most familiar. Adding a large, high-resolution monitor to your computer array gives you a graphic interface that is intuitively easy to navigate and control. Keeping that monitor working well, or replacing it when it's time for an upgrade, can help you get the most out of the programs you run.
Cathode-ray monitors produce images by scanning across the screen with a variable electron beam. Keeping that beam in motion, thus preventing screen burnout, and running the scanner at a frequency high enough to simulate motion, requires a well-functioning flyback transformer. This unit, which occasionally wears out and needs replacement, dampens line power and raises the power cycle rate to produce a controlled stream of electrons resulting in a high-resolution image on the screen.