Nothing actually. A strategic default is just a name for people who walk away from their home/or property but they call it a strategic default or a business decision. Cut your losses jeopardize credit score for the short term and move-on. A business loss. A strategic default is for people who can afford to make the payments but no longer want to because the property value is less than their mortgage.
However it may seem strategic but in some states the banks can still collect 10 years later. In my opinion you are much better off trying to negotiate with the lender short sale or trying to hold on to the property then walking away strategic or not.