This is a good method for setting large tiles and where mortar build up will be over 3/4" of an inch. Most LHT (Large/Heavy Tile) thinset mortar is only rated to be built up a max of 3/4". Using Deck Mud or Dry Pack sand and cement mix will allow you to build up as much as 2" thick if needed. Also, setting the tiles in a fresh bed of mortar will allow you to easily adjust the tiles as you go and they will not slump or sag. I have several videos on the how to mix and use deck mud or dry pack mortar.
The use of large porcelain tiles is very popular right now and there is a misconception that the larger the tile, the easier it is to install. It is actually just the opposite, the lager the tile the more difficult it is to avoid lippage (one tile sitting higher or lower than the adjacent one). Using the method shown, will also avoid the need to use expensive leveling systems.