@dustsweepers helps you claim all your rewards. For example I just upvoted you. My upvote alone isnt enough to get you past the $0.02 threshold needed for a payout. If my upvote ends up being the only one on your comment then you will not get paid for the upvote I gave you once the 7 day payout is reached. The potential rewards get turned to dust because you dont get them.

What @dustsweepers does is just before the seven day payout .. it goes around upvoting all your comments that have an upvote on them but the rewards are below the payment threshold. This is to push the rewards your comment receives past the $0.02 threshold to make sure you get the rewards that were intended for you on each comment.

Short version

You are basically paying a bot to upvote your comments ( with your own funds ) that already have upvotes on them so you dont lose out on the small rewards attached to each comment.