When using mysqlcheck, the -o and the -C options are exclusive, yet this is not documented in the man page for mysqlcheck.
o --check-only-changed, -C
Check only tables that have changed since the last check or that have not been closed properly.
o --optimize, -o
Optimize the tables.
Yet if you specify both:
Error: /opt/zimbra/common/bin/mysqlcheck doesn't support multiple contradicting commands.