ive plastered shitloads of kitchens and never once have i leveled it off first...
worst ive had to do is throw a bit of bonding on the splashback area before tiling...
i take it your mate aint no kitchen fitter...
bathrooms are a different story cos they tend to be tiled all the way round at least a metre high and a lot go up to the cieling...a real bitch to tile if its not something like flat so i'll bond them out first...and stop there...tiles do the rest...
kitchens have adjustable brackets and end panels you can trim...all units should be screwed together and levelled before you fix em to the wall, worktops shouldnt be scribed in - youll lose the drip, worst case - bond out the splashback, the rest you cant see..