I switch frequently between 3 different scales of bass. I have both a lined 34” fretless and an unlined 34” fretless, a 30”, and a 23.75”. I switch between them according to the needed tone. I also have a much easier time playing chorded passages on the lined fretboard, especially when singing at the same time. With multiple strings ringing at once, and keeping a lead vocal going, I can use all the sensory input I can get.
Plus, the scale changes (especially going from the 23.75” to the fretless 34”) become much easier when I have a reference point. In almost all songs, I seldom look at the fretboard, but I’ve grown to know when I’m most likely to need the extra visual at particular points in the song. I find lines quite helpful. Don’t always need them, but I’m glad I have them on one of the basses,