Dual-cable brake levers were often used on tandems to apply the rim brakes, with a single-cable lever on the other side for a hub or disc brake. As others have mentioned, getting both cables to properly engage both calipers can be tricky, and not always satisfying. At least on a tandem, there's little risk of face-planting if the front caliper is overly applied. A common modification was to run single-cable levers for the rim brakes and a bar-end shifter for the hub/disc brake to function as a "drag" brake on long downhills, Or, give the stoker their own lever to run the hub/disc brake. I can't see any real advantage to using a dual-cable lever on a single bike, unless one of your arms has been amputated (and I have set up bikes like that for amputees).