You can click on the checkbox and make your post. It is an attempt to encourage members to start new threads instead of posting a new related question in an existing thread.
but having several threads about the same topic can be confusing. i think the search function wont be very effective like that. you will find 20-30 thread about a topic.
It is actually simpler to find relevant search results when each thread is specific to a single question. This way each question has its own title and you can immediately see whether the thread is relevant for you or not.
Finding relevant posts in long threads is more or less impossible.
I think it is useful but also annoying . I would set it at least to 2 month.
Also, sometimes a new thread can be the best choice, but not so rarely add a post in an old thread can be better (and I know that for this reason you can "force"...)
1. It is easier, at least for me, to discuss a question when it is confined in a single thread.
2. It is much easier to find relevant threads while searching, when each thread covers exactly one specific question. This is a critical point and is the key for building a useful knowledge base.
This is one of the reasons that Stackoverflow is such a useful resource.
The ideal thread structure is:
First post with clear title and one specific question.
Few posts with suggestions or clarifications if needed.
Last post with solution.
Later if someone comes and asks a follow up question in the same thread then the thread is no longer easy to follow and no one will ever find the follow up question. Instead the new question should be posted in a new thread (maybe with a link to the other question).
There are few cases where it does make sense to post in the same thread. In those cases you can click on the checkbox and post.
I agree totally with Erel here and I don't understand the discussion. It is only a warning and can be overridden with a single click.
In the past I prefered all questions related to one of my libraries in the libraries thread. That was because I often hadn't the time to read all questions in the questions forum. Now I changed my mind and think it is easier to have each question in its own thread. Simply because the forum doesn't have a "Search in thread" feature.
Some library threads have now 30 or more pages. If I know that there was a solution posted somewhere in the thread that is now asked again it is not easy to find the solution that was posted on page 37 of 69 for example.
Well, reading this thread now I think that the best solution would be to permanently close the thread (lock it), inviting the author to add [SOLVED] to the title.
If someone asks a question without having first searched on site, you should answer with a link to the relevant thread, and a day later you delete this new useless thread.
Different members use different language. So the "useless" thread can be actually useful as someone might enter a search term and find the newer thread and then follow the link to the more important thread.
I think that closing all threads is a bit too aggressive.
I wanted to add an option to mark a post as the "answer" post. However I didn't find any forum addon that worked good enough.