so your eyes go zig-zag from the taller glyphs of the word to the low glyph of the underscore (vertical zig zag motion), instead of jumping to the next world (horizontal).
funny, I was just checking because I have never noticed my eyes doing that and afaics my eyes still scan horizontally. I don't need to look down to see the underscore. I guess YMMV?
word+empty-space+word
but
word+line-down-below+word
so your eyes go zig-zag from the taller glyphs of the word to the low glyph of the underscore (vertical zig zag motion), instead of jumping to the next world (horizontal).