'--opt' is used override the mysql server's normal method of reading the whole result set into memory giving a faster dump.
c:\mysql\bin\mysqldump -u root -p --opt myDatabase > myDatabase.sql
'-a' or '-all' (either will do) optimises the dump by creating mysql specific CREATE statements that speeds up the restore:
c:\mysql\bin\mysqldump -u root -p --all myDatabase > myDatabase.sql