Lady C, marcusjb is correct. Sleeping on a 400 is very pleasant and makes the event more enjoyable. In my 1.0 guise I always slept on 400s (well, on the Brevet Cymru, my only 400, and the Snowpocalypse Easter Arrow, somewhat too deeply). The transition to 2.0 with optional sleep occurred on Brevet Cymru 2015, when I knew I'd not wake up/start again during the overnight deluge. Stress, adrenaline, and survival instinct kicked in (and the need to complete a PBP qualifier).
So I'd suggest you aim to sleep and only carry on without if you're able to do so safely and something forces the decision. It really is much more civilised, as you say.