The major problem with the flash sales sites is they provided very little upside to the business offering the deal. Taking a small hit in a 50% off deal could be considered part of the cost of customer aquisition if the customer comes back. However a very large segment of the flash sale demographic are not desirable repeatable customers. The deal is clear, they're there for the large discount, and probably will only be back if you give it to them again.
They work best when you have a very inexpensive product where you can still make a profit by doubling your MSRP then selling for "80% off". Doesn't do wonders for your brand though, which is part of why the company I work for which has been doing this for the better part of a decade is trying to move away from the model.
