I think it would be a good idea for there to be when a mod locks a thread it should delete it. So we do not get soooo many locked threads clogging the back of the forum.
Then a lot of users would lose posts and complain in the forums about it.
I think something similar to this was suggested before, but instead of it being deleted there would be a forum for all the locked topics. I'm not sure if it was accepted or declined, but that's just unnecessary work. The locked threads will fall to the back of the forum pages, they're not annoying people.
Not to mention the most used reason for locking a thread instead of deleting it is because it holds an answer to a question or because it has to serve as a warning to other people about making such threads.
If they are deleted, more so if they are deleted before people know why it is getting deleted, there will be some seriously angry people around. Not to mention I have several locked art threads, that are locked because people would otherwise post in them, making them necro threads, but there is absolutely no reason to deleted them, as no rules have been broken. Also, post counts.
