Quote from Daal:
This is no free lunch. the discounts happen in hard to borrow stocks, usually the short rate eats your profit. It it doesnt its because your broker happen to have shares avaliable
Definitely it is the cost to borrow, it will usually end up costing you more money than you could make, unless your broker somehow has cheap shares to short that no one else does which doesn't make sense to me because someone would be losing money somewhere. These could be helpful if you held some of these beat down shares long and you could 'lend' them out using the SSF to capture the high borrow rate to recoup some of your losses if you planned on holding on to these companies for the long haul.