Every creator has different needs, so you get to decide how much control you want to keep and for how long, and how much to give away.
Creators often want different amounts of control depending on the kind of work of it, the audience and the time.
So if you wrote a poem, you might feel differently if another poet wants to reproduce your work versus if an ad agency wants to put it on a billboard. If you created a sculpture for a grassy, undeveloped park, you might feel differently if the park board decides to put in a wooden bench right beside your work and uses it for promotional purposes for a fast food outlet. Depending on the work, you might also feel differently about how it’s used now versus ten or twenty years from now. Check out the Creative Commons toolkit for some more information.
Legal tip: If somebody gives you a contract and it has the words “assignment” or “transfer” in it, that likely means if you sign that contract, you will lose the copyright (and therefore lose control of the work). This type of assignment, or transfer, is made possible by Section 13 of the Copyright Act. That means you will no longer be the person who decides how your work is used. You might want to suggest a license instead. Find out more about the difference here.