As a junior officer you start to make your mark by proving ability - not only in primary duties but also all those other aspects of Service life. Once promoted to Sqn Ldr (or equivalent) then your career will be " managed" and postings will be "arranged" both as a confirmatory test and as a means of broadening expertise needed for VSO rank. It definitely starts to get political at sqn ldr and gets more so as one ascends the greasy pole.
I managed to get off the pole by PVRing to emigrate having been put on the selection board for the next one up! Spoilt their career roadmap totally!
PS As one of the last ones to take the 'C' exam I always thought it was a mistake to get rid of it - served as a useful filter.