When publishing your data and code, it's crucial that you apply a license. A license is a document that acts as your official permission for others to do, use, or own something that you are the copyright owner for (like code you've written, or data you've gathered). It's a crucial part of scholarly communications -- your colleagues need to know exactly how they can use your materials, and you can establish boundaries that you are comfortable with. Releasing your materials without a license creates ambiguity.
Licenses exist on a spectrum from totally open (like CC0, a license that says anyone can do anything with your materials and don't need to cite you -- it puts your materials in the public domain) to more restrictive (like CC-BY-NC-ND, which says that anyone can use your materials as long as it's for non-commercial use, they don't make any derivatives, and they attribute you). You can choose a license that you are comfortable with -- there is no one-size-fits-all solution. There are licenses that have no restrictions.