Billie said that he usually writes his songs acoustically then they beef them up with all the other instruments later, so this is effectively like hearing the 'original' version of the song.
Homecoming is my favourite song off American idiot followed by Jesus of Suburbia. I love these two long songs, I love all the different sections. Homecoming is a super well-written song and even having sections written and sang by the others (even Tre's section) add a lot to the song. Jesus is definitely more iconic but if they busted out Homecoming at a live show I'd probably lose my shit.