It really depends.

Fully agree on the expense controllers bit: we aren't 'allowed' F - but on one BA sale the one way upgrade, meant that F (booked in A) was cheaper than CW (booked in J) by c. £2k. Took over a month for it to get approved.

Back on topic - Semi-Flex are good when you're booking in advance and then client plans change ... and you end up pushing back trips. I've just taken a ticket that was originally booked for travel in mid-July; it got changed 4 times, and then net cost to me for all the changes was £7. Definitely out weighs the extra £80-odd quid that was the diff between non-flex and semi-flex fares.