A daily deal site is all about discounts. Getting a service at half off the usual price – what could be better? The answer is, of course, getting even deeper discount.
And here come promotional codes. Whatever "unbeatable" price you offer for the deal, you may also offer a few more percent discount on the top of it by issuing a promocode.
On Getsocio you can create a promotional code, which can be applied to any deal in a given timespan. Then give the code to existing or potential customers via any kind of marketing campaign, the more viral one, the better.
See promotional codes guide for details.