Yes, it´s just for effect.
It´s as if someone the singer having a trademark of sorts, this guy may have used that also to go with the instruments, if you think of it he kinda makes it go with the guitar, or as if it was the guitar-like sound in the end of the singing.
Other singers use it purely for effect, if you see Kid Abelha (Paula Toller) singing at 1:50-52", you can see that the word "importanteee" wasn´t sang that way, perhaps the music was another thing altogheter. https://www.youtube.com/watch?v=Gv82iaSC ... _qAzeF37k5
And there are the singers that like to "toy" with their voice, like Elis Regina, Alcione etc...Making "experiments" in their singing, what let it all the more colourful and interesting. And even more difficult to emulate.
Be careful with music, it can be deceptive sometimes, they sometimes use a neologism that is unique of a certain era, of a certain group, etc...They may use not standard English, etc, it´s good, but with moderation.