Yes - stop the merging of threads!
Old threads lost in the depths of the forum should be left alone. Combining them to newer threads adds little, when most of them have lost the attachments; links given in old posting to sites that no longer work; links in postings to other threads that were working, but now don't work; and bookmarks to new threads vanish when they are merged with the old threads.
I'm not sure what prompted this merging of the threads, but please stop.
(Just one user's opinion. 
)
With regards to thread merging I do feel it is in the boards interests to have all threads on a subject under one 'roof'.
For example, when doing a search for a particular model, you may come across 20 or more different threads and who wants to search through all of those to see which is the best one to add something to? Having one thread for each Model/Subject just makes more sense to me.
With regards to two threads about the same person having different 'themes', does it matter? Since both threads are indeed about the same model anyway. In those cases the threads are renamed to reflect the different aspects of the separate threads, or given the simple title of the model herself merely with the word MERGED following it.
There was also a mention about threads which go 'off-topic', threads which start of about a certain model then divert onto something else. The fact that this happens in a thread about a model is really of no consequence really as many threads do this and then come roaring back 'on-topic' later on. I have on occasion separated out such discussion from threads, but in the case of very long threads, you can't sort through every post just because it goes off-topic somewhat.
Anyway, in the vast majority of cases MERGING threads has none of these sorts of problems and lets people find information on their favourite models so much easier. Indeed, in many cases I have merged threads in which the titles don't even mention the model in question! In these cases it is much better for the members as it prevents multiple threads springing up when people DO do a search on a model and find nothing. One such example is a thread that was entitled 'The New Lucy Pinder' which was about Casey Batchelor, so it was merged with another Casey thread and renamed.
As Pal points out, it is a rare thing to have two active large threads on the same model at the same time, and even if we do, it will not stop me merging them.
Still, if you have any problems with 'off-topic' portions in threads about models, please let me know and I can always excise them to tidy things up.
There is of course the problem of once a thread is merged, then the bookmark can be lost, but popular threads are usually added to pretty frequently, so finding them again isn't too much of a hassle. In any case I will be updating a MERGINGS thread in site issues to inform members of any mergings I do.
Finally, the subject of lost links (when someone links to an image attachment rather than re-uploading it). This is unavoidable I am afraid. I carried out tests and when merging threads together any pictures from the LATER thread, automatically have the TOPIC portion changed to the OLDER thread. The newly merged thread will always keep the OLDER topic number (the lower of the two topic numbers). The age of the thread is determined by the date of the very first post. Which of course will change the reply number of any attachments, breaking internal links. This doesn't cause that many problems, but it may be annoying should post an internal link. This happened to a few of Pal internal links when I merged a couple of 'Amateur babe' threads together. A few of the amateurs had been linked to in the ID thread and when the threads were merged, the links were lost. However, for the most part mergings are for model threads rather than specific threads so these sorts of occurrences are quite rare.
Mod edit to edtiorialize a wee bit about salem's final paragraph above: by "internal links" salem's talking about when a user will use the "[IMG]" tags to embed and display a linked image inside the text of a post. If the source of the linked image happens to be in another BEA forum post, we refer to it as an internal link since both the original attached image and the new display of it in a more recent post are local: i.e.: located internally on the BEA server.
I did happen to have roughly 20 such internal links broken due to thread mergings, but I probably do that internal linking more often than some other users, since I generally use an internal link to display an image that another user has posted elsewhere in the forum when I add that image to my IDQ thread: http://forum.bearchive.com/index.php/topic,9991092.0.html I'm not going to lie... it was time consuming to re-find and re-link all those broken images after they were merged, but that was the only alternative to just leaving them broken/undisplayed (which my OCD wouldn't permit 
).
If you find that a merge has broken a link you put elsewhere in the forum by changing the URL to the internally-sourced image, you can usually find it with a bit of searching, or sometimes it's just easier to find the image file itself on your hard drive or online and re-upload/attach it. Despite this collateral damage from thread merging, we (forum mods) STILL prefer that users don't upload the exact same image file again and again over time since it only wastes server space and needlessly embiggens the attachment database. IF you want to display an image that another user has already attached to a post here (thus, it's already on the BEA server) please STILL use the internal link method (i.e.: the "[IMG]" tags) to do so. Thanks. 
-Palomine