Interesting reading on author rights by Timothy Armstrong. An excerpt follows:

There are good reasons to retain your copyright rather than assigning it to the publisher. Why might you prefer this?

• They don’t need it. Publishers can do all the things they might legitimately want to do with your work (publish it, put it on their web site, advertise it, submit it to the major databases, offer it to other authors for commentary, and the list could go on) without owning the copyright. You can grant all the permissions that are necessary to make their publication perfectly lawful. A variety of standard form agreements exist to accomplish this.

• Flexibility. You probably can’t anticipate all the ways in which you might want to use (or reuse) your article in the future. Years from now, you may decide that you want to post it on SSRN, or convert it to a book chapter, or update it to account for subsequent legal developments. If you own the rights to the work, you can do all those things. If you assigned away your rights, you must negotiate with the original publisher. Perhaps they will grant you the permission to reuse their work (remember, if you assigned away your copyright, they own it) in the manner you wish. But, at a minimum, it introduces inconveniences that would not exist if you retained your copyright.