On one particular project from 1995 where the hardware was very cost optimised, the C program compiled to 1800 bytes which meant we could save nearly a dollar by buying micro-controllers with 2KB flash rather than 4KB flash. We manufactured 20,000 units with this cheaper chip. 2 years down the line we needed a simple code change to increase the UART baud rate to the host, a change that should have resulted in the same sized binary, but instead increased it to 2300 bytes due to a newer C compiler. We ended up tweaking the assembly file and running an assembler, then praying there would be no more changes!

I have always over specified the micro-controllers a little from that point, and kept a copy of the original dev environment, luckily all my projects are now EOL as I am retired.