For me, it's less about declination, and more about setting bearings. It's still more of a convenience thing, though, but a pretty huge convenience in my experience.
When off-trail hiking through woods, fog, mist or rain (no landmarks), as fast as possible, it's easier for me to keep an arrow centered in another arrow, than it is trying to keep the arrow pointed at a particular number - you have to look down/hesitate more, and end up moving slower as a result. This is especially true when it's dark and you're navigating rugged terrain.
I remember when I summited Mt. Jasper in the Indian Peaks Wilderness via the NE ridge on an after work hike. I miscalculated the time it took, and ended up returning to treeline in the dark. I knew I had to travel on a particular heading to hit a river, and could then follow the river back to a loop hiking trail, which would then take me to the trailhead. I can't imagine moving as fast as I did, by headlamp, around cliffs, down steep gullies, over deadfall, across marshes and small streams, while trying to keep the compass arrow pointed at a particular number, as opposed to keeping the it centered. I would have been a lot slower.
I was late for my dinner date, but I might have completely missed it and been in big trouble if I had to keep a closer eye on the compass.
Again, still a 'convenience' thing, but in my experiences, being able to move quickly isn't always a minor convenience, especially when you're on a deadline. For example, summiting a peak, or crossing a pass, before thunderstorms roll in.
Another lesson learned from that experience, is that when navigating rough terrain, having a lanyard on your compass is really nice - you can quickly drop it and use both hands to get over/around obstacles like deadfall. This is particularly useful in some areas of the Gore range, which has a nasty amount of deadfall in areas (and very few trails).