I DO NOT like to lunge for the purpose of tiring a horse out, but it does have its purpose I believe. I like to lunge for at the most 5 min and that's usually always at a trot. I believe it gets the horse to focus on me and I can judge their attitude/disposition that day. I don't like to just go around and around and around. I do lots of changes of direction to keep the horse focused and listening for my next move. I also like to lunge for a bit when I take a horse to a new place and they might be a little nervous. Once I lunge, they usually settle down, they know the routine.
I think it has a purpose, but that purpose is not to tire the horse to a point that it only wants to walk.
Yesterday is history, tomorrow is a mystery, and today is a gift-that's why it's called the present.