What are the consequences of using Sci-Hub?
It's of questionable legality, but it's not going to lead to prosecution. For me personally using sci-hub has led to new research results in fields outside of my specialization that will (very likely) appear in leading peer reviewed journals. One problem I'm not sure about is whether it's wise to say in the acknowledgements: "I thank Alexandra Elbakyan for setting up Sci-Hub without which the research results reported in this paper would have been impossible", in an Elsevier paper.

Using sci-hub therefore has at least the consequence of your personal scientific enlightenment, and possibly even of many other people who benefit from research you have been able to as a result of using sci-hub.