Some schools will absolutely encourage students to apply way ahead of that deadline. If you have mock exams in November though, it seems daft to make you apply before they've had a chance to review those results and potentially adjust your predicted grades.
BTW, it's a UCAS rule that universities
must consider all applications received before the deadline equally. They can do this in a few ways.
1. They can make offers as and the applications arrive. This only really works if, from experience, the uni knows that the particular course is never oversubscribed and so won't run out of places.
2. They can not make any offers until after the "equal consideration" deadline. This is typically called the "gathered field" approach, where only once they have all applications in can they start making offers to the best.
3. They can take a hybrid approach. They could set a grade threshold above where anyone who applies with those grades (or above), regardless of when their application is received, gets an offer. Anyone who applies with below those grades, it put into a pile to review after 31 January. This still counts as "equal consideration" because
when you apply doesn't impact whether you get an offer of not. Your grades dictate that.
(King's take approach 3, generally, looking at
this spreadsheet for 2023 applicants which shows "date decision received" in column E.)
The only real benefit you get from applying early is that (depending on the approach you target unis take) you might get an offer earlier than you otherwise would. For some, this "peace of mind" justifies applying earlier.