Since there are a couple of comments about SQ here may I add a little clarification.
SQ look after their premium passengers very well and the PPS Club is a long standing programme. Krisflyer on the other hand was introduced in 2000 when SQ joined the *A. SQ have never made any bones about the fact that they are not at all interested in the Krisflyer programme nor its premium members any more than they are interested in *G members of other programmes.
In other words if you are not a PPS member don’t expect anything other than the possibility of redeeming points for seat they can’t sell and no PPS member wants. You can only earn PPS status in First and Business class which clarifies for those who may doubt where SQ priorities lie.