Back buttering or back trowelling

[Dumbo]

Question is at what size tile do you guys stop back buttering and start using a notched trowel on the back of the tile and for arguments sake lets say the background is good

 

[Bond]

Depending on the situation anything above say 600x600, may consider using 6mm notched trowel on the tile.

 

[Italy]

I agree with bonds
and I would like to add,
with thin tiles, use trowell

 

[Flintstone]

600x400 on the job I am currently on and I am back troweling. 12mm on wall and 4mm on tile. Could probably go a bit less but using clips so a thicker bed is good for me.