I watched a horse tied to a fence panic and pull back, bringing half the fence with him and banging up his knees. If he'd been tied to something breakable like baling twine, he would have saved both himself and the fence. I do like to tie to something that will break, in saying that though, I've known several horses that have learned to pull back and free themselves just for the sake of it. In those cases, I think they do need to learn to stand tied to a solid object, since they've developed a bad habit. Something elastic that they can pull against without hurting themselves, but will always encourage them back to the fence. It seems gentler than tying them to something solid and letting them learn the hard way that they can't break free.
However, I acknowledge those who prefer their solid-object tying, and see the merits of that too. It's just not what I'd do.
"When the power of love overcomes the love of power, the world will finally know peace." - Jimi Hendrix