Without a voting period, there is no incentive for people to play and provide feedback on the games. So far I've had 1 person provide me with feedback when I'd usually get at least several.
I know the voting is kinda BS anyway, but I tend to enter jams so as to get feedback from people, and that usually comes from the voting period -- how you get rated for categories via voting is usually helpful. Plus, I believe you can have categories like: fun, design, aesthetics, originality, etc. You don't need to have ultra specific areas tied to your jam or some theme that people can vote and provide feedback on. You can use the voting categories to get an impression of how your game comes across to people and where your weak areas may be.