The SEC 179 and Special Depreciation Allowance have nothing to do with safe harbor. SEC 179 allows you to fully depreciate a qualified asset in the tax year it is placed in service. The Special Depreciation Allowance allows you to depreciate 50% (or more or less) of the cost in the first year placed in service. It's just what you might call "accelerated depreciation" (but not really). Those assets still add to your total cost basis and you still have to recapture and pay taxes on that depreciation when you sell the property assets.
Typically, since long term residential rental real estate already operates at a loss on paper at tax filing time, for many the SDA and SEC179 make no difference in their overall tax liability in the year claimed. But for some it will add to the losses allowed against "ordinary income", which is maxed at $25K for a tax year, provided your AGI is not over the threshold for that tax year, and you actually have the taxable "ordinary" income to deduct it from.
