I think grandparent's idea was to first play only measure N, then measures N-1 to N, then measures N-2 to N and so on. Not literally play the sheet music backwards.

Yeah exactly. If you learn a song "traditionally" you have to play gradually longer passages until you hit the part you haven't learned yet. This will make you very proficient in playing the beginning of the song but you will usually always stumble towards the end. If you learn "backwards" then for each new measure you learn, the rest of the song will be easy, since you've already learned it.

To make sure I force myself to practice all parts of the song with the attention each measure needs and complete the piece only if all measures were mastered "perfectly" (i.e. as good as my level at that time allowed).