I'm redoing a 4' x 5' bathroom with just toilet and sink, no steam or wetness issues. I am down to the OSB and its flat. Want to know if I can just screw the 1/4" fiberock down and put 14" square tiles in thinset on top of that. I know there is alot of talk/arguing about yes/no on thinsetting it down. What do you think for a small bathroom that shouldn't have any water issues and the relative small size of it? It's 3/4 inch OSB. and larger 14" tiles rather than 4"x 4" or 12" tiles. If thinset is cheap and easy to do I might just do it, but if it doesn't matter, then why?
The industry insists that all cement board be installed in a fresh bed of thinset then mechanically fastened. That's what keeps tile from breaking and grout from cracking. It has nothing to do with OSB or the size of the tile or whether or not you want to cheap-out all over $7 worth of additional thinset mortar under the tile backer or how small or large the area is or whether or not you have water issues.
It has to do with completing a long-living installation.
...there is alot of talk/arguing about yes/no on thinsetting it down
NO THERE ISN'T. Never has been. That has been the industry standard for a long long long time. There is no arguing.