Because Maths, is only learnt through the hard yards, practice practice practice.
You can never expect to go in, and come out a grade better?
Correct me if Im wrong.
I actually disagree, maths is NOT learnt only through practice. Yes, some is required. But on the whole I think that profound understanding is the best way to improve, once you have a grasp of the basics(Which, incidentally, don't require question-spamming either...). Not only to secure marks, but also just to have knowledge of what you are doing, why you are doing it, when to apply it, what its limitations are and a host of other essential information, that is only chanced upon when question-spamming.
I do agree, though, that doing some questions in repetition does help to familiarise yourself with the question-types that appear. This is good when doing the textbook exercises where you
know that they are all going to be of the same basic type. But I challenge you, when doing the exam, is it actually beneficial to be so overly familiar with the question types that you have seen that, instead of reading each question like you have never read anything similar to avoid missing information or misinterpreting the question, you have the preconception that they are of the same type you have read in your earlier studies?
No. This is very bad.
But, haha, I have gone a bit over the top. It does help, but, in addition to my earlier comments, it leaves big holes in your understanding.
And after you have a deep understanding I don't think you have the need nor the desire to do many many questions.
Going to lectures provides a different perspective on the maths. This helps to broaden your understanding. Also it can help to clarify some of the basics. I'm talking dirt-level basics; the fundamental stuff. I know personally I find that it is in these areas that I am most likely to be unsure. (At least it was true for Methods last year). Going to lectures goes over basically the whole course(TSFX is better for this), so it can show you clearly and without fail, as the lecturer covers all the relevant material, what you need to work on.
So apart from these things there is little else on offer from a lecture.
With Derrick Ha's lecture, though, he challenges you to take it into your own hands. The lecture is a starting point and the rest is up to you.
While TSFX said "remember this!" and when a student questioned the mathematical rationale behind it, the lecturer said, "never mind; you probably won't understand it anyway." This kind of attitude disgusts me. While some people may choose to merely memorise 'what to do', it is not TSFX's prerogative to deny the progression of a students understanding.