Back window gasket

[Harleyhop]

I am new to posting on this forum but have reviewed many post's.i love all the great advice and information you guys provide! I have a 2014 3500RE that has a foam gasket in the back window that has come unglued and looks like it's falling out of the track. Does anybody know what it's for? It doesn't look like it seals anything. It looks like it was stuck on the inside of the track not towards the window side. I'm planning on gluing back but not sure what it's for.
Thanks for any insight on this!:)