Why declare your ball unplayable?

Answer 1

You have to take a penalty drop, which is two club lengths from the nearest point of relief. The nearest point of relief being no closer to the hole.

In fact for a ball declared unplayable you have 3 options:-

1) Return and play another shot from a point as near as possible to where that ball was last played (stroke & distance).

2) drop the ball within 2 club lengths of where the ball lies, no nearer the hole.

3) Drop as far back as you like keeping the position of the ball in line with the flag.