As we already know keeping a normal terran unit inside a dropship prevents that particular unit from being converted to a special unit.
But what if we can't get a dropship and still want to get income from the source? This video explores how you can get income and only converting 2 units as consequence. No quick reflexes, or sequences of inputs needed. Just land Sci Facility 2 squares gap below the doodad.
So far I can see this being a great use for taxing Netherlands while you get to keep all but 2 of your dropships. It's also great use when you don't have a dropship. It is also great use as a safety measure in case you lose your dropship with the loaded unit.
For taxing same type specials with higher hiearchy it is advised to build an ebay 1 square gap below the doodad and do a quick lift/land instead. This is because ebay is cheaper and builds faster