In this video, inventor/contractor Phil Green tests six different substrates to see if back-buttering tiles really makes a difference to the coverage on the back of the tile and in the long run, to the probability of a more permanent tile installation.

Disclaimer: This "test" is to see if a visual difference of thin set coverage can be noticeable between identical tiles being set on six different substrates. The only difference between the tiles is that one has been back-buttered and the other has not.

This is NOT all inclusive. real world installations are subject to deflections and stresses that may reflect a different result.