What does the drip edge do?

[Buishi]

I'm just finishing up a platform, and considering how I'll attach the

insulation

. I'm doing the

insulation

rather unconventionally, using batts of rock wool
, which require a bit more support than bubble wrap or a blanket. I'm considering having the insulation wrap around the outside of the platform, instead of resting on top of it, but I'm undecided, partly because the drip edge would now be on the inside of the insulation, and I'm not sure if that would cause a problem. In the picture below you can see the two different scenarios. The reason I'm looking into option 2 is it's a very small yurt (100 sq ft)' and 5.5 inches will make a difference.

Another question, is there a reason not to have the yurt canvas wrap underneath, pulled together like a drawstring?

https://www.dropbox.com/s/k42cyehvzv...urt%20wall.png

Long story short, I don't know what the drip edge actually does, is it necessary?