It is always important to reference your work. That is what any writing instructor can tell you. This is important for both your own sake and for the sake of the people whose work you are using. A list of references or reference materials allows you to give credit where it is due. This is not just a professional consideration, it is a moral one. Those who have put in the time to research the facts deserve credit for the work that they do.
It is for this reason that references are often used to improve the quality of a paper and failure to reference material properly can result in a charge of plagiarism and, effectively, end a career. Students are often expelled from schools for plagiarism or failure to appropriately reference their work. At the very least, a student who is found guilty of plagiarism will get no more than an F. And they will not deserve any more either.
It is for this reason important that students properly reference their material. But it is even more important that professional researchers do the same thing. The other scholars and researchers who put out information depend on these references to demonstrate the value of their research and, with new developments in technology, it is becoming increasingly possible for researchers to track just how influential their work is.
This can be inspiring, but it can also help justify tenure. It is for this reason that researchers, scientists and scholars should always be committed to giving credit where it is due rather than passing off referenced work as their own. It is uncertain whether or not the scholarly professional will begin moving toward open source research. It might be possible for scholarly work to become available to everyone.
Only the future will tell, but even if all information is free, it should only become more important for people to say where they got the information that they are using. After all, it will be easier to find out if they do not.