I’ve used it in the past when having flash memory blocks that could change but you need the compiler to put them into flash memory and not RAM. It’s mainly to get the compiler to stop assuming that it can optimize using the default value.

I’ve recently had the opposite: code worked then the next day without anything changing it didn’t.

Turned out the J-Link programmer always needs the license check to work, but that expires every day at midnight. It only prompts again if you choose the app and restart it. So I couldn’t get my debugger to work and spent hours trying to figure it out until I did the best thing. I turned it off and on again.