Total rubbish, this makes me so angry!! I use this method near enough all the time, its the only way you can get your tiling absolutely perfect. Now I don't just mean 5 spots, I mean on a 300 x 600 tile I'd put 18 spots + ! I only use rapid setting, cement based adhesive and I can guarantee that once set, you will not be able to remove that tile without pulling all the plasterboard with it! I know, I've had to do it before, when I've made a mistake. No timber wall is ever 100% level and flat (to the mm) and even with some self levelling, floors can be 2/4 mm out so to get the job perfect, you have to spot. I've been tiling this way for 13 years and I've only ever had a problem with 2 floors and that was down to the dodgy, cheap plywood! I've even ripped out old jobs of mine and my fathers, and it's been a tough job. No cracked tiles, no "moisture damage" and they're well stuck! I've ripped out jobs where the previous fitter has combed the wall and the adhesive has hardly touched the tile, you can see there's a space between each adhesive line left on the wall so there can't be 100% coverage can there!?
So, all in all, this talk of "cowboys only dot and dab" is total garbage talk. I've never seen a job as perfect as mine, ever! Walls absolutely solid and floors absolutely solid...perfectly level and flat!
The old boys are spot on with what they say, it's all about marketing and £££'s!