When the same chord is played several measures in a row, the beginning of each measure will still be marked with an underline even though there’s no actual chord change.

Let’s have a look at an example:

F
Listen as your day unfolds
G                   Am7
Challenge what the future holds
F                                G    C
Try and keep your head up to the sky
F
Lovers, they may cause you tears
G              Am7
Go ahead, release your fears
F                                  G
Stand up and be counted, don't be 'shamed to cry
C
   You gotta be

And its one-pager counterpart:

Notice how every first line in each pair of lyrics has an underline to mark the second F measure of that line. To the contrary, in the traditional chords above, there’s nothing to indicate how the lyrics are aligned with the second F measure.

Check out this example for instance:

F          Am
    It's a god-awful small affair
Cm         D7
    To the girl with the mousy hair
Gm          A#
    But her mummy is yelling no
C7
    And her daddy has told her to go
F           Am
    But her friend is nowhere to be seen
Cm          D7
    Now she walks through her sunken dream
Gm         A#
    To the seat with the clearest view
C7                                         G#
    And she's hooked to the silver screen

Notice how, in the corresponding one-pager section, daddy and hooked are underlined to mark where the second C7 measure starts on these lines: