The people screaming the loudest over voter-ID requirements are black activists. Since blacks tend to vote overwhelmingly Democratic, folks there might be want people to be counted, even if they can't make it to the polls.
If you work under the assumption that your black constituents vote Democratic, you're doing them a favor for voting for them, getting someone to vote for you in proxy, saying that they're you. It they happened to be Republican...well, you just covered for their craziness and got the correct vote down.
If turnout turns out to be higher than normal; you can chalk it up to good GOTV efforts. You just used alternative methods to get it out.