Ed,

The Pre-Chorus serves a specific function in songs that have maximum emotional impact and a "dramatic arc."

Also called the "rise" it shows the perspective lifting, or shifting, often a "glimmer of hope."

Like This:

V1 (Down in the dumps) Maybe C, F and Am

Yeah I have the blues
I hate the news
broken and broke and walking in the rain
and staring at my busted shoes

Pre Chorus (Maybe Em and F now)

But I know that somehow, some way
one day, I will sing Hey, Hey Hey

Ch: (Up)

So Hey hey hey,
Hey Hey Hey
I'm finally singing
Hey Hey Hey

Without a Pre Chorus you might have:

V1 E7

Got the blues
danged dirty blues
nothing going on
but blues and the news

CH (stay on E7)

Oh yeah blues
talking 'bout blues
12 bars, no car
talking 'bout those no car 12 bar blues

(really long pentatonic solo)

Got it???

smile