It just takes up precious time and slows down computers and servers. If you see these spamming messages, just ignore them or delete them. Threads Threads usually starts with an interesting subject that people like to comment on. If the subject is interesting, there will be a lot of replies. These replies add on to the thread.
Some threads are only two or three messages and some go over a hundred.
If it is something people like to comment on, the thread will go on for weeks. People start threads everyday. By posting different threads, there are more subjects to read about and comment on. It is up to the individual whether he wants to post, reply, or follow up to messages. As for the comments in the threads, it depends on the individual writing it.