My boat's rudder is about 5 or 6 feet aft of the prop, so there's a delay between the time I apply a burst of power and when the stern kicks over. The bow thruster tames that, and makes it much easier to maneuver in tight spaces. It also helps guide the boat's direction in reverse. There's got to be increased drag when sailing, but I don't notice it. My boat's builder says the (properly faired) bow thruster doesn't affect speed significantly. I don't race so it's not an issue.

It also came with electric winches, which I thought I wouldn't use. Boy, that idea died quickly. That's like thinking you wouldn't use a remote control for the TV, before you had it. It's a real convenience, and a work saver that's appreciated even more when it's hot and humid.