In Chas Hodges (of Chas & Dave) book he wrote about this, and said that at their sound-checks they got the vocals right first, then added in everything else underneath it so that the vocals always stood out clearly. He did say that a few times they had to advise the sound people that pretty much no-one ever went home from a Chas & Dave gig complaining that they couldn`t hear the bass drum properly, but a few times people had complained they couldn`t hear the vocals, so from then on that was how they worked, they vocals/lyrics being more important than any of the accompanying/supporting instruments.
Which is directly opposite to pretty much every sound check I`ve ever done, where probably more time was spent on the level of the kick drum than on (all of) the vocals. Ok, yes, it was punk, but even our vomit should be heard clearly!