Among other things, it's designed for longer drain intervals, so it keeps the engine clean longer.
Volvo, in particular, recommends an A3/B4 for sludge removal in neglected engines.
Most of the oils that meet MB 229.5 (for the MB in my sig) also meet A3/B4.
It's a good choice for longer drain intervals, or engines that are hard on oils, or create sludge.
I wouldn't bother using it in my Tundra, for example, but I absolutely use it for the longer drain intervals in my three turbocharged Volvos and my turbocharged Mercedes.