Quite possibly, this is the most important lesson in the whole two years. Integration is the invers of differentiation and a huge chunk of the course is about finding different ways of integrating. It is important at AS, but it's really really important in C4. Most students find it the most fulfilling part of the course because when you solve complex problems, you get that warm glow inside.
I know you may find this hard to believe, but I actually think that this is the worst thing I've ever seen on YouTube.