Gmx order: sliced v. permolecule

GROMACS version:2020.3
GROMACS modification: No
What is the difference when using gmx order with permolecule v. sliced? With -permolecules yes, I get a sliced.xvg output with the same number of columns (16 because may lipid has 18 carbons) and lines (168 that is the number of molecules), that make sense because it is the S per molecule. However, with the -sl set to any number, I do not get a sliced.xvg even using -os. What exactly does the -sl option does?

Thank you,