Logical and literary concerns more than search engines, I think. If we have an ongoing discussion on the effects of peace marches, it's easier to have a discussion that people will follow if it's all in one thread.
If we go on to a certain point where John Q makes a statement, and then John R starts a new thread to respont to John Q, it breaks the train of throught and bifurcates the discussion.
I suppose the main reason John R started the new thread is that he not only wants to state his opinion - he wants a headline on the front page to go along with it. The Forum menu is our "front page." There are times when we need an editor to make sure no one reporter gets too much space on Page One.

It's even more important in the discussion of a particular song. If all the information is together in one thread, it's easier for the reader to get the entire picture.

It is a search matter, too - if the results of a search are scattered all over hell and yon, it takes a heck of a lot of effort to follow up on all those scattered pieces. Better to have things a bit more cohesive. Also - facts are easier to search for than concepts are. If it's a philosophical discussion, you'll never find it if it's all in pieces.

-Joe Offer-