Wow this is great, some really good and detailed advice there, thank you!
In a certain way i love the metronome, cause it gives you structure and it’s nice seeing things work out, even if you slowly increase speed. I like to concentrate on carefully practicing cleanliness, and i even more love the results as nothing is more satisfying than nailing hard parts cleanly.
But useless to say that it needs lot of time, patience and self-discipline, and this is the part where i struggle sometimes, because i try to play it faster than i actually should too often.
And once you fall into that unclean, fast playing, you have to restart and go back to a slower tempo where you can play it right.
But if you are honest to yourself and keep being disciplined it’s one hell of a method to get better, because seeing actual results in bpm-numbers when you manage to play faster and faster but still clean, gives a load of motivation! 
So to answer the title-question: doing good if you use it right, harm if you do it wrong, that pretty much sums up my experience
