Mike Dougherty-384281 (12/8/2012)
Another good reason to be replaceable is that you should be able to "hand off" to a coworker so you can advance within the organization. If you've built yourself into a role so completely that it would be painful to your employer to move you up, then you'll be stuck there until you retire.
Excellent point. Not much fun watching your colleagues get all the interesting projects and training courses while you are shovelling albatross turds simply because you've gained the knowledge to stop it pecking.