Skarpi, I think I have answered your question regarding the derivation of the song but I never commented on whether it is used for funerals or weddings. In all my experience of this song it has never been used as a funeral or wedding song in particular although some folk might like to use in that way. Tannahill's song was sung by my mother about 70 years ago but just "as a song".
Vellbekomme!(Jeg kan lidt dansk ogsa Svensk og Norsk.)