The problem is that sometimes you have to do impossibly steep descents at comparatively low speed (below 250, somewhere above 225 or so), for example at non-radar controlled airports with high minimum crossing altitudes - unless youre visual you will be stuck high up and unable to for example make a straight in ILS (we got a couple of airports like this in our route network unfortunately) - speedbrakes are useless at low speeds, and flaps 5 and 230 knots just work so brilliantly
