At a wild guess, that you may upvote a comment that you support – but there's a second part that you wouldn't agree with. Or that people should split up their comments so that people can upvote/downvote individual parts?
Hi. I'd like to buy 51% of your stake of this upvote at 2x the current market value. This is an investment proposal and you have to accept now, I don't have time for negotiations as I'm an important businessman conducting business.
Rest assured me and my firm will not use our majority hold on your upvote to change or sway your held beliefs or writing style. Our lawyers do advise you that we absolutely have this power, though.
I think OP is referring to comment where multiple talking points are made, but you can’t selectively apply your upvote/downvote to specific parts of the comment. You either upvote it all, or downvote it all.
So if I start talking about how pineapple is ok on a pizza, a downvote for this take also means you downvote how I’m trying to clarify OP’s message.