If you don't take the minimum depreciation that you're supposed to take, the tax laws say when you sell you must reduce the basis for purposes of computing gain/loss by the depreciation you took (allowed) and any additional that you should have taken (allowable).  so you will end up paying taxes on that amount even though you never deducted it.   say it's  $4000,  your tax bill could go up by $1000 and that's ignoring any state taxes.  this is not unique to real estate. it applies to all depreciable property.