I know a guy who feels strongly that la, la, las and na, na, nas are a sign of lyrical laziness. But I disagree.  What kind of song would The Boxer be without the lai, lai, lai-s right? I contend that some songs are stronger for their da-de-dums. A place for simply feeling the song without sorting through lyrics. Of course you have to have some decent lyrics too. Weak lyrics and a patch of yeah, yeah, yeah is like eating at Olive Garden (is that a basket of hot dog buns?).