Also, I always earth-ground outside generators for stage power since it's way too easy for power cable's hot wire to be pinched and shorted to a grounded stage. That can flip the entire distro upside down with the Hot at earth potential and the Ground/Neutral at 120-volts above earth potential. If that happens, then it's way too easy for a musician holding a properly grounded guitar to get a serious shock if they touch a metal stage or wet earth. That's why I always insist on the stage being bonded to the generator's neutral-ground point.
This is probably the best argument I've read for grounding generators and bonding to other metal in the vicinity.
To clarify the "flip the entire distro upside down": without grounding, the line and neutral from the genny are effectively floating, meaning that there will be 0V between line and dirt, and 0V between neutral and dirt, since there is no complete circuit via the dirt. (I use the term 'dirt' here to clearly show that I'm not referring to the equipment grounding conductor or the frame of the genny.)
But if the line of a floating output inadvertently gets bonded to dirt, i.e., by pinching and piercing the insulation, you now DO have a complete circuit. Because of this bond, line-to-dirt will be 0V, and neutral-to-dirt will be the line-to-neutral voltage, typically 120V. With the neutral bonded to the EGC at the genny (but not to a ground rod or other grounded system), the EGC is also at 120V to dirt.
So now when Joe Vocalist reaches for his "properly grounded" microphone, he completes the circuit and gets zapped.
On the other hand, if you ground the generator's EGC to dirt, when that cable gets pinched it trips a circuit breaker or GFI instead of lying in wait to electrocute someone.