When you click on “User CP” doesn’t the board have to search for your subscribed threads the same way it would for “New Posts”?
Again, just curious, not complaining. 
It probably doesn’t have to search for your subscribed threads, instead they’re kept in a table associated with your user ID. Not knowing how vB implements it but that would be my guess.
Apparently what Telemark says is true because when you go to “Quick Links” and click on Subscribed Threads, that doesn’t count as a search either. For which I am eternally grateful. (Hint: [del]if[/del] WHEN the stupid board resets your last visited time so that CP says you have no new threads, you can go to quick links and look at all the subscribed threads that have new stuff in them.)
I’ve never looked in quick links, so that’s helpful to know it’s there.
If you use CP and don’t get any new threads, there’s a link at the bottom that says “show all subscribed threads”. Easier than Quick Links.
It’s probably because it’s a very quick database lookup. There is likely a table which contains a column for thread id and another column for subscriber. Doing a lookup like “Find all entries in Subscriptions where Subscriber=Shakes” is relatively quick.
When you search for threads using a text search, that is much slower. You are looking for substrings. A query like “Find all threads which contain the word ‘Jupiter’” takes much longer since much more information needs to be searched and the substrings searches take longer.
Thanks to you, Irishman; I never saw that subscribed link down there. Now we both learned something this week.
On the other hand, the “find all new posts” button is implemented via a search, even though that one could be done by a quick, efficient lookup, too.