I suggest to have a check-box beside each topic to be able to mass-delete topics. As time goes by, there are many topics that grow old and carry no relevance for the preset moment. One can safely delete those by just looking at the title and/or the number of replies. For example, in my forum there is an introduction forum where people just introduce themselves. Now I just need to allow those posts to stay there and delete later, as it wouldn't be of any value later. There are many topics in other forums too, which have no value at the moment.
I'm listing some topics from my forum as a example. Most of these were created in late 2005 and early 2006 and I have not seen their content. I just randomly picked them. Now from search engine perspective, it's highly unlikely that anyone is going to land on these pages as they have very vague or absolutely no keywords. From the user perspective, it is also very unlikely that a member will even be tempted to read the thread, forget going through 12 pages (each having 50 topics). So by allowing such topics to stay, I'm simply wasting a lot of resources and creating a mess later.
I agree that there is some risk of losing some good posts but then we are building a discussion forum with limited resources and not a knowledge base. I have seen that members don't even bother to use the search function and keep asking the same thing. So there is a probability that the lost topic will be covered again.
Another bother would be regarding memberships. Any forum owner would agree that there will exist a large percentage of members who are just lying there only to inflate the member count. It would free up a lot of resources if there were a solution that would identify and remove users that have not made a single post or logged in the last X months.
Thanks for listening.