White playing at either point e threatens to cut the two black groups apart. Each of them only has one eye, so they will die. Black must respond at the other point e. The value of this threat is more than 40 points.
This is actually a discussion that should be added under "counting" or estimating" rather than here...
If I take chinese counting, saving the Black group is worth
Total value: roughly 60 points, rather than 40. Am I wrong?
And if I just consider the total area covered by that Black group, I can count at least 36 ten, giving a swing of 72.