When software is released without a license it is released into the public domain. Public Domain software has the following liabilities:

• The first person to license the software is the owner.
• If someone else takes your software they can restrict your use of your own code.
• They can sell your code and not give you a penny

Therefore it is important to license your code. If you license your code under an Open Source license:

• You are designated "owner" of your code
• No one can restrict your rights to use your own code
• You can release later versions of the same code under new licenses
• You can release the same version under other non-open licenses (used in the dual licensing business model)
• You can sell your software and charge whatever you like

If you work on an Open Source project and you make alterations to a codebase you have the following rights:

• Are owner of the altered code
• Depending on the OSS license of the original code you may be able to license your code in whatever way you want
• You can distribute the code to whomever you want, and charge whatever you want for the altered code