It will lower your HOC by the thickness of one blade (.203" or .250").
It also lowers the cut plane of the blade with regard to the deck skirt.
Some mowers have blade spacers that you can remove to compensate. DC was one of these. With DC being about the only ZTR with a manual PTO, this was often done with great results.
If you do a search for double blades, there is literally a weeks worth of threads to read. Dating back to this forums infancy.
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