There is really no short and simple way to cover this, other than perhaps to say to following. Copyright, publishing agreements, and terms of licensing all have significant value and can (and arguably should) be factored into your negotiations.
The importance of this point cannot be overstated, and understanding it in depth may well be critical to your career sustainability. Copyright, publishing and licensing agreements are your assets just as your keyboard, guitar, computer or car are assets. They all have a value and their value needs to be factored into your agreements.
Every composer will need to find a solution that is right for them given their professional relationships, experience and track record.
Copyright, publishing and licensing are complex issues to get across, especially when you are early in your career. Want to know more? Then read on.