It's something several acquaintances of mine who are published, successful writers subscribe to. One recently summed it up nicely as "plan the mountains, write the valleys".
The major advantages are that it gives you the ability to write the ending first, so you don't get to the end and discover that you need to dig yourself out of a hole, and that you can keep things internally consistent, ensuring people don't magically teleport around the world (unless of course that's actually a thing your characters can do).
There's something to be said for not over-planning, but also for giving yourself enough time and room to be able to spot problems ahead of time so you don't write yourself into a corner.
That said, I'll add you to my list of people to contact when they start being published (probably end of next year).
I essentially put planned waypoints on the plot map, but they just took their own sweet time in getting to them. I had to burn someone's house down, to make them pick up the pace.
I view it a bit as one of those aerial racing games where you have to fly through the rings that define the course. As long as the characters pass within a certain radius of my planned plot waypoints, I don't have to murder any of them to keep them in line (until a character death actually is one of the points). The smaller the allowed radius, the more control you have to exert over the characters to hit the mark, and the more they start to feel like marionettes animated by the author instead of people acting on their own impulses.
So I definitely had an ending (plus cliffhanger) in mind before I started. I allowed the amount of narrative it took to get to that ending be a variable. I was actually surprised when one of the supporting characters I wanted to put in the next book parted ways with the protagonist and wasn't there for the ending, but I couldn't do it without making someone act inconsistently.
I once discovered that one of my lead characters had an estranged daughter by reading what she'd said off the screen after I'd typed it.
What made this one get to some semblance of done is that I forced myself to write 1000 words a night. And the bulk of it was horrible rambling string of consciousness crap. But it force me to exercise the writing muscles. Then I later just filtered out the crap, and luckily found a couple of good lines here, a neat character there. And it sort of just worked out. It's making a habit out of it that really counts.
I think people sometimes imagine the planning approach means more or less writing the entire story as an outline first and not being able to let your characters surprise you, but that's not really true. Some of what I had when I started writing boiled down to "important subplot tied into protagonist's past starts somewhere around here"; it turned out that subplot ended up not only bringing out some of the important themes and riffing on devices in the main plot, but it ended up tying back into a previously published story. I like relatively dense plots -- the novel is science fiction, maybe a bit closer to the hard sf end of the spectrum than the space opera end, but there's a lot of mystery elements -- and playing around with structure a little. At least for me, those are hard to pull off in a satisfying way without laying the groundwork ahead of time.
*Classically this is three-act structure, but nearly all modern descriptions of three-act structure, especially in screenplays, talk about how the second act is roughly twice the length of the other two and has distinct halves. I call that four acts. :)