Well the example given is decoding JSON. If that is happening in a long loop, you can yield once per loop and be safe. Not all problems are neatly broken apart like that, but in those cases how much of a chance does the server have to not timeout regardless, you know?
Note that once per loop might be too often, but you can just measure how long a loop run typically takes and compare to how soon you want to preempt the task, then yield at the right interval.
