You will have the option of responding to a few (two?) 150 word essay like questions in in the supplementary application form. I do not remember the questions, but one might have been why Cambridge? So I think you should wait for that. Also it is not required that you do the SAQ essays as many students have received offers without doing them. I think the tutors recommend that you write the SAQ essays only if you have something valuable to say that your PS didn't cover (usually geared towards Cambridge).
Only part of it is optional, you do have to complete most of it. I didn't do much for it - I wrote a few sentences on why I'd like to go to Cambridge for one of the questions, and nothing for the other.
(Original post by safwaansh)
did you do a additional PS?
Yes - if you mean the additional 1200 characters (with spaces) that you are given on the SAQ, then yes. I just said why the Cambridge course was best for me and why the other ones I had applied to weren't. And also said a little bit more about the additional reading I'd done. I in addition said why certain options were appealing and why I wanted to study at Cambridge per se.
NB: There are also questions on your career plans and how you have kept up the interest in your chosen subject outside of school / college work. I would advise answering those two as well. May as well. Then there is a final question asking if there is anything else that you would like them to know.
I wrote a little bit explaining why the Cambridge course and teaching styles particularly appealed to me, as obviously this is the sort of thing you can't put in your PS (especially when applying to science-orientated Cam and practical-based Notts).
Oh, and I didn't exactly plan it. I just started typing when I filled in the SAQ and put anything that seemed relevant.