Not really. You make more money as a department head in certain areas but as a co manager you have the option to become a manager and climb the corporate ladder. It really depends on what you're comfortable with. co Managers get moved around a lot too.
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Would you like fries with th... I mean, your milk in a bag?
It's probably worse honestly but if you want to move up you have no choice but to take it on or else you'll be stuck as a dept head forever never making much more at least if you go to co manager you have a shot at going higher, maybe getting into the office or even going to another company where you'd probably make more.
Than. Then is an adverb indicating when a given action takes place. Than is a conjunction linking two elements in a sentence. In this case: co manager and department head.