If you are the seller your list agent should do the same. In either case both buyers and sellers should know there is a back up offer in place and that is stated by the addendum.
As a seller there is nothing better than having more than one buyer want to purchase your home. The added "insurance" means that buyer #1 will have a little more pressure & less flexibility in any further negotiations, since there are other buyers ready to step in and make the purchase.
As a buyer, there is no down side to be in the Back up position as you can terminate at any time and move on to another property. If this is a short sale situation, then often the back up buyers who may come later to the deal are the ones that ultimately get the house. I say to my buyers - if it is the right house, then lets try and put it together.
What is your agent advising you?
I work with buyers and would be happy to help you further with this. Get in touch if you are interested in my help.
Good luck to you.