It tells Pegasus Mail not to look for a Netware connection (quicker startup?). 

It is harmless to run without the -A switch but there is no reason not to use it if you aren't running Netware.

What does the -A do when executing PMAIL from the command line?  I cannot find it in the User Manual

From Help > Commandline options:

-A (no parameter)
Forces Pegasus Mail to run in standalone mode, ignoring any NetWare connection.

Thanks Brian, and what does that imply?