Pros? You get some limited protection if there is damage.
Cons: none - you get people who have enough credit rating on their cards to hold an authorisation against potential damage.
If you want zero protection and attract the wrong type of people, then set it to zero. Otherwise pick a sum that you are happy with. Remember it is not charge to the guest when booking - just an authorisation against their card in case of difficult.
Is this true? I have read it is not an authorization but in fact they reserve the right to charge the customer if there is damage. Furthermore I have read the terms and have posted my own question about missing items.