Why do many songs contain the word "yeah" and especially in lives ?

[george1234]

I have even seen Kaori do it in Yume no Tsubasa live

https://www.lyrics.com/lyrics/yeah

it feels like that when the lyricist is out of words uses this one lol or its a way to pump up the audience excitement

 

[ritardando]

Because vocalizing around with yeah yeah and nananana makes a great filler for a buildup or before/during instrumental solo. And it's easy to project your voice with yeah yeah yeAAAHH