Publicly available data sometime still carries restrictions. These may be presented in a "click through" agreement that you agree to (don't we all) as you breeze by. This is important for data that may be still unpublished/under analysis. A common restrictions is that you can't use that data for an independent publication (especially if it is still unpublished).
In short, you would want to do due diligence, before assuming an accessible dataset is public and running with it.