What's the BIG DEAL about your skylight's bottom pan metal?

Here's a skylight with a missing bottom pan! NOT GOOD

You can see at the bottom of skylight the raw wood! Had this person used a bottom pan metal, the skylight curb wouldn't be leaking. You can tell by the blue tape that homeowner recently painted the skylight well. (I dunno if he he did it well or not, he just painted the skylight well) And now, the bottom corner is leaking. It was not leaking for the longest time because the roof underlayment prevented water from coming into the house, but with years of service, the underlayment finally deteriorated and gave out.

By the way, this is an older skylight and the seals are pulling away from the corners. 

Location: Beaverton, OR