How did it work? Did they drive up to a box or hand the ballot to a poll worker? If it was just dropped in a box then it seems no worse than mailing or other drop-off methods. Once poll workers are in the chain of custody, things get out of hand (and into a dumpster), especially in heavily dem areas.
None of this was happening with drive thru voting. Show up, drop it off and away you go. Much easier for ballot harvesters.
Extra ballots or secondary ballots can cause major trouble for legitimate voters, having their election day vote rejected or nullified due to an illegal ballot.