No bother at all!
The information from: man su
-, -l, --login
make the shell a login shell
A mere - implies -l. If USER not given, assume root.
And googling around, I see this diddy.
"The - option establishes a default environment for the user."
So, if I just type: su fred, I am not really in the same place as if I typed su -l fred or even drop the l and just su - fred.
All you really need to know is that ( su - ) is what I always use so I don't have problems locating programs and commands as the root user.