On a lot of the boat pictures i've been seeing lately the aluminum tab on the outdrive behind the prop has been cut off. Advantage ? Disadvantage ? Why is this done ? Bo don't know!

The tab is there to negate the prop torque. If you have power steering, hydraulic, or counter rotating engines it is not necessary. If you run a higher pitched prop sometimes clearance to the standard tab can be a problem. It is zinc by the way and there is usually a large zinc insert in there that lays flush for corrosion protection.