> What's an example of typical application code that will behave differently with the mitigations on or off?

Pretty much any application where there is limited execution time budget. If it takes too long it's considered broken, unusable, undesirable etc. Any realtime-ish stuff.

Ad bidding, video processing, audio processing / messaging, industrial control systems, robotics, general signal processing, logging systems that will now be overwhelmed and drop messages, databases that will experience timeouts and retries, scientific computations that will now take weeks more to run and potentially screw up other projects.

But hey it's a great time for Intel. Hey, psst, over here, I got a faster later gen CPU for you, for an easy price of $999.99 to bring you performance back to where it was last week.

Certainly the speed of it's execution. That could be difference enough to be concerning when shifting from dev to prod.