Hi all,
Renovating an existing bathroom, including the replacement of an old cast iron bathtub with a new one. I plan to tile above the new tub for the surround, as well as the floor.

When I was doing the demo on the bathroom, the tub was resting directly on the subflooring, below the 3/4 plywood that I'm replacing also. Would there be any reason to put the new tub on the subflooring only??...I suspect the 3/4 plywood was put in during a previous renovation, but I'm wondering if this was done intentionally for any reason.

Thanks in advance for any help.
Sam