I've tons of objects with material applied directly on front face (none on back) but not grouped.
(this has no effect on TheaRender that no considers backface)
In Enscape I've big problems with transparent objects. Default material in backface results visible and often ugly.
I can re-open all of my objects, group them by material and re-save them. But it is an hard work and I hope it will not necessarely
My +1 to "no rendering" on back faces with default material