Being on rails just makes things a bit too predictable and boring. That is why I always keep it "flexible", while making sure there's at least some kind of a vision present.
As long as I'm meeting deadlines and checking off one list after the other, I'm good.
In business I've found extreme focus is the way forward and there's little room for much else. The same can be said for a lot of roles people take on, military for instance, flying passenger aircraft, drilling on off-shore oil rigs. Getting off the rails in jobs like that ends in disaster.
What I'm trying to say is it's situational.
In a person's personal life there's often a little more leeway to be less structured and that's something I do a great deal. There's a time and place for both.
It is situational, indeed.