If you do your own prep ( installing Cement, foam or plasterboard on walls or boards on floors and screeds) then you take your time and get it right so you don’t need clips if the tiles are good. If you have bowed tiles then clips can help straighten tile till adhesive has a chance to dry and fix-in place permanently. If the in situ walls are to be used then clips can help with lipping but you must make sure you are not creating voids behind tiles and if walls were that bad then would be better to fix first then no need for clips. Clips are in my van only for odd occasions, just another tool that is an option when weighing up sub surface, materials, tiles etc