mycambridge separate personal statement

The additional statement is purely optional. It's probably more there for applicants to the rather more unique courses at Cambridge e.g. land economy, HSPS, natural sciences, ASNAC, where the applicants are likely applying to more common/conventional courses elsewhere. If you don't have anything additional to add there, don't put anything - it will not disadvantage you.

would you reccomend putting it for HSPS? I've mostly talked about politics and IR in my application, but I'm wondering if I should talk a bit more about anthropology or sociology - I don't really have too much to say however. Do you know if it would disadvantage me to not do it - Ik they say they don't, but I'm wondering if, for a relatively niche subject like HSPS, I should still write somthing.