Why and why add site copyright when copy-pasting?

Question

Copyright

And really, why do that? Is there any real benefit from this? And in the end, even the code from such sites is copied and pasted with copyright. Is this done specifically to complicate the life of site visitors, or is it for the illusion that site materials are protected by such a talisman and no one will stupidly copy them for easy rewriting and output to the network under a different authorship?