The protection resistor limits the amount of current the op-amp can be asked to source/sink. This can prevent the op-amp from being destroyed if, by accident, two outputs are connected together.
There are two configurations for the output resistor: one that causes slight voltage drops and results in pitch inaccuracies (used for most of my modules which are unlikely to process pitch CVs), and a more sophisticated one that does not cause voltage drops (which I use in modules generating/processing pitch CVs like Yarns). The configuration that causes pitch inaccuracies has a slight positive side-effect, though: it allows passive summing of outputs.
Bypassing the protection resistor has two negative side effects:
- More risks of damaging the op-amp through incorrect patching or ESD, since the output pin is directly “visible” from the outside world.
- If the circuit surrounding the op-amp does not attenuate high frequencies (for example, for example, in an inverting amplifier, no additional capacitor between V- and Vo), you can get ugly ringing and self-oscillation when long lengths of cables are patched to the output and/or when you connect the output to modules that have additional filtering or ESD protection on their inputs.