Porcelains are tough as old boots so unlikely to crack even if a screw was over-tightened. Ceramics on the other hand are more prone to cracking if fixings are over torqued. My preference (and its just a personal preference) is to overbore holes at 8mm on porcelains then push the rawl plug beyond the
tile into the substrate. I let that take the weight of the fixing rather than the tiled area.
But I am not sure what would be the worse force at play. Is it the downward force of say a fully loaded bathroom cabinet resting on a plug that would pull down on a
tile. Or is it the over tightening of a screw?
What I do try to do on both ceramics or porcelains is:
1) dont over tighten screws.
2) The plastic rawl plugs I use tend to break up if screws are over done anyway
3) I dont think any real harm can come with weights of things on a
tile. Most loads are spread over a few screws (even robe hooks have two screw holes)
4) As a matter of course I tend to push the plug beyond the
tile so that the screw hangs in free space out of habit.
5) that using 365drills (rather than a spade drill) to bore a hole into any
tile causes a the hole to become a cylinder (not a cone) so the hole is actually very strong and unlikely to chip out or break up. Even the backs dont blow out.
So the result is that the hole is as strong as it can be.
You can see evidence of the strength of the sides of the holes in the pic above by looking at the larger holes.
So there you have it. I use diamond drill bits to form perfect little cylinders in all tiles. Then push plugs beyond the
tile so the weight of the article hangs in the air and I dont over tighten screws.