"Allow Free Signups?" should be set to "Yes" if....

1) This is a free product, and you wish to publish a DAP-generated free signup form to sign up people for free to this Product, say, so you can get their email address and market to them via email.

- OR -

2) This is a paid product, BUT you will still be publishing a free sign-up form just so people can sign up themselves for your paid product. If you wish to reduce the number of people signing up for this paid product via a form, then you can make it a bit more restrictive by requiring them to enter a valid coupon code during sign up (something you would've created in advance, of course).

- OR -

3) If you're not sure, just simply select "No" for now and you can revisit this later.