I thought that this might boil-down to the usual fire code/building code
type of mumbo-jumbo...
So many people within so many square feet of space... bla,bla,bla

But still.... a 120 inch span (10') of a single floor joist would be
about 1/3rd inch up-and-down play... that seems (to me) like a heck of a
lot of movement... tile fooling or not!

But, I guess, that's withOUT adding the strength of the subflooring
that will tie the joist together.

Am I right or wrong?
David