For me, almost purely nostalgia. As silly as it sounds, meeting goals I set for myself when I was 12. (Plus a sprinkling of convenience; the scan-doubler lets me use a leftover flatscreen instead of a hulking CRT, ethernet saves me a lot of heartache transferring files from my desktop, etc).

But mostly just games. I didn't really play games from roughly 1995-2010 for various reasons, so Amiga (and megadrive) are still where a lot of my old favourites are. Thanks to Catalina, my desktop can't play civ5 anymore. But my Amiga can still play civ1!