I've ridden a wide variety of boards. With a 10.5 foot, i find a waist width of 25.5 or larger nescessary.
Wide boads can be just as agile as regular boards... if designed right. A lot of companies just take their standard board, widen it, and expect it to act the same. You need to increase sidecut a little bit to account for the additional width, There is a VERY slight amount of additional time to transition from edge to edge, and with a slight quicker sidecut, it's entirely unquantifiable.
Wider boards are less hooky coming intoa landing or just in general riding around as they tend to get your edges that much higher in the air. Easy enough to deduce as well, just look at the mathematics of triangles. Flat ground is the ground, angle is the angle of lean... wider board is going to be the same a longer leg on the triangle, giving you that much more clearance.
Pow float is increased... boards are typically faster due to better weight distribution accross the base material... the list REALLY goes on.
Disadvantages are an increase in board weight, and if not properly designed they will turn slower than their regular width equivalents.
Overall, I don't know the industry runs such skinny boards. More companies are transitioning into mid-wide size boards... but so many companies are still way behind.