I’ve gone the other way. Had some really wide (for me) On One Fleegles (716.7mm in length), really liked the way they made you feel on the bike, wider arms, slightly forward, the attack position as described above. Also found them better for cranking up climbs.
However as nearly all my riding is in or involves woodland in some way wider bars were a bit stoopid, I was forever getting hooked up on branches/undergrowth and having to stop to wheel my bike between trees which my XC bar widthed mates would flash through like the speeders in return of the jedi, irksome.
So cut them down a few weeks ago, originally I wanted to take a couple of centimetres off each side ended up having a bit of a brain spasm while cutting and they ended up at about 630mm. Bums I thought – way too narrow, I’ll have to buy some new ones. I gave them a go anyway and what a revelation sooooo much better (obv.) in the woods but I found I could carve better turns too – maybe because I could get lower because my weight was higher in relation to my leaning angle – I’m aware that this is probably because of a skill deficit on my part. I also felt faster when pedalling although this may be subjective due to the racer position. My hands/palms also felt less sore I guess due to the fact that my weight wasn’t so far forward.