I use my A1200 to test my game ports (I actually do the coding on the PC).
I also use it for retro gaming (WHDLOAD), playing demos and playing my own game ports (extended beta testing) and I love customizing WB (OS 3.9) to see how good and how fast I can get it.
Finally I like adding new hardware to my 20 year old Amiga (eg HDMI output)