He’s not a good public speaker anymore so using him in that capacity can be a risk. After all, it’s what engaged the collapse of his campaign.
One way it could make sense is if they use him as decoy to distract Trump. Biden gets back up on stage and Donnie will jump on all of his old Biden cracks. He won’t be able to help himself and will be like a dog on a scent. None of that matters anymore and it’s all wasted time and energy on something that is not relevant to the election.
Important Time Saving Caveat:
I’m clarifying my point here and not trying to debate, argue, or convince you anything other than what you believe. That would be an impossible task and a waste of everyone’s time. I happily cede the last word to you in this discussion.