Asking back, when I limit the outgoing connections from a network, why would I account for any nonstandard port and make the ruleset unwieldy, just in case someone wanted to do something clever?

A simple ruleset would only block a couple dangerous ports and leave everything else connectable. Whitelisting outgoing destination ports is more complicated and more annoying to deal with for no benefit. The only place you should be whitelisting destination ports is when you're looking at incoming connections.