Screams are a skill that have to be developed, just like any other skill, including singing normally. Not just anybody can do it, at least without screwing up their vocal cords. It takes a lot of time and effort, which is, unfortunately, not truly appreciated by large portions of the community. I often hear it called 'just noise', which is far from the truth IMO.
I see screams as essential to metal music (Metal, not screaming shit for the sake of screaming). However, it has to be controlled, developed, and essential to the song. Screams offer a different sound and characteristic to a song than clean vocals would. If they're just screaming for the sake of screaming, then what's the point. I can't stand listening to those 'singers' that don't do it properly and destroy their vocal cords. You can tell rather easily they haven't put in the effort to learn how to perform a scream, and it ruins the song from a musically technical perspective, in my eyes.
Lamb of God's songs would not have the same effect on the audience if they were performed with clean vocals. That's not a dig at Randy Blythe's cleans, I really don't know how they would sound so I'm not going to comment. Their songs portray an emotion of frustration, anger, dissatisfaction at the world, that wouldn't have the same intensity with clean vocals.
That's not to say cleans are bad. I enjoy them as well, as well as a combination, such as Between the Buried and Me, or the Human Abstract, to name just two. Screams add a different layer to the music, as do growls, as do cleans, and as do other singing styles.
Here's three metal songs, each belonging to very different genres of metal. you can clearly hear the different is styles, and how the chosen vocals affect the song.
Combination of screams and growls, adding intensity to an already hugely technical song.
(Band: Born of Osiris. Song: Recreate)
Combination of screams, growls, cleans, and even a hymn-style choir.
(Band: Devin Townsend Project. Song: Planet of the Apes) P.s. Tommy Roger's vocal growls are heard from 6:36.
Screams, growls, and clean vocals for the chorus (which are really quite good, IMO)
(Band: Sylosis. Song: After Lifeless Years)
