There's no way to "do something wrong" with Spot Lock. It's either off or on.

As jimp advises, its accuracy is no better than the GPS technology that "remembers" where the spot is. Unless I missed something, iPilot's GPS does not use WAAS to improve accuracy, so that means "the spot" has a diameter of about 30'. Product literature says the motor activates when the unit drifts more than 5' from "the spot". If you're drifting fast, you'll be much farther from "the spot" before the boat starts moving forward again. At this point you could be anywhere in a circle with a 50'+ diameter.

Spot Lock has its time and place, and that's not going to include small BPs or windy days. Also, you shouldn't work too close to docks or anything else you can't afford to hit.