I worked as a roofer for about 6 years. That strip you're referring to
is a reinforcement strip used to give the nails (staples when I was
doing it) better hold-down qualities. You're not supposed to peel
anything off. There will be a row of what looks like dashes along the
bottom of the shingles. These globs heat up in the sun allow the
shingles to stick to eachother. This is very important in windy
conditions. I've seen entire roofs blow off in the cold because the
roof was newly added and they didn't have a chance to "bond" yet.

I only remember this strip being on what is called "dimensional"
shingles. I don't think 3-tabs have it. If they do, that's a new
develpment since I last worked as a roofer.

wrote:
I seem to recall the last time I did a roofing job (11 years ago), I
recall removing the thin plastic film on the glue strip, which I
assumed was there to prevent the shingles getting all stuck together in
the bundle.

However, I'm roofing a new shed and this film is really tough to pull
off - not to mention messy. It'll take me longer to pull the film
strip than lay the shingles.

Question; is this designed to melt/dissolve; i.e., can I leave it on?

Note that the glue blobs don't have the covering. In the bundle
they're lined up with the plastic strips on the shingle above, on the
roof of course, the blobs would be under the covering shingle tabs.

thanks.