As everyone else has said!
But also benefits in looking at the mark scheme in seeing just how many points are awarded for initial steps. I work with someone who is hoping to pass, and she was quite surprised when we went through one of her papers against hte mark scheme, just how many marks she was able to get even on questions that she really didn't understand at all! (I am not sure this is a great thing in terms of the integrity of the exam and what a grade 4 actually means, but it's definitely worth knonwing).
Also some very common things that don't get part marks are spelled out. Like finding percents of a number; initial steps that say things like 10%=8 don't necessarily get marks, because you haven't shown that you divided by 10 to get it. (If you get the final answer right, that's fine, but it doesn't count for part marks if you don't, on at least one of the boards).
So learning things like that is useful, along with things like how to set your work out clearly - often one final mark for actually stating an answer to a question "yes he has enough money" or whatever.
So loads to learn from mark schemes and examiner reports, far more than just the 'did I get the right answer'. It's really helpful to know how many marks there are and what they are far. Students often say 'oh I'd have got 2 out of 3 on that I'm sure, I was close' - but not close in the way that would get marks. Other times, they might put something down to start, having no real idea how to continue, and that would get them an extra mark. The more you understand how the mark schemes are, the more you maximise your chances.
For targeting work at different grades, many revision sites have it split into categories for each topic, so you can literally google things like "linear equations grade 5 gcse questions" and have suitable things come up.