It is a mixture of both - I am the only one that usually renames or merges threads.
Reasons are obvious - because when you have the same type of thread, it is better to merge them, hence the same topics under three threads, especially if they fall over to a different page, aka Rise of the Footsoldier topics, or Olympia Phil Heath topics (six of them the same thing).
Easier to concentrate them together then having all of them all over the place
I don't delete content unless it is plain harassment or stupidity, but tend to merge them of they are the same topics, etc