In harvesting peas today, I was able to compare peas that grow on the ground to the ones supported by a tomato cage. Production is about equal between the two rows of plants, so that's not a reason to stake or not stake peas.
The main advantage in staking peas appears to be how far you've got to bend to pick them. The ones that have been supported are much easier to get to than the ones on the ground.
Puckdropper