Also making the fare Flexi will increase the SP earn, which might might be useful if near requalification or other threshold (banked year).

My recollection is that the economy SP earn is non-linear - so a Flexi H/M/B/Y fare has a better SP/$ than sale and saver fares. I don’t think this is true for biz (but haven’t mapped them out fir some time).

Annoying for TT flights, Flexi is an add-on fare product, and not an actual fare class change, and so earns no additional SP.