Making a poll open to everyone, even if they haven't registered, makes it very accesible to everyone to participate
in it. But this has a small disadvantage. Since there is no User IDs to track the votes, it might be easier to "hack"
a poll so that you can vote more than once, without much technical knowledge.
This means that if the results of your poll are not very important (i.e. "Should we eat pizza tonight?"), you probably
don't need this option activated. But if you wish your poll results to be much more reliable, you may consider activating
this option, even if it means forcing your users to having to register into the website.