Jaký je rozdíl mezi `su -` a `su --login`?

Ruční zadávání Debianu se zdá být srozumitelnější:

   -, -l, --login
       Provide an environment similar to what the user would expect had the user logged
       in directly.

       When - is used, it must be specified before any username. For portability it is
       recommended to use it as last option, before any username. The other forms (-l
       and --login) do not have this restriction.