When I was working for a foundry consultancy, we did the following
- Download routines to add delays when writing certain tracks. This was a security feature. When the program started, it would try to read that track normally. If it could, it failed the security check and stopped running. If it couldn't, it downloaded the delay and checked again. If it couldn't then it failed security again.
- Download routines to do database searches and return the results. This was amazingly fast. 4 seconds to search the entire floppy. This was before SQL was invented so it was a home brew pattern match written in 6502 assembler.
- Make the LED flash different colours when computations were running
What other obscure tasks were the 8050/1541 drives used for?