Answer:
Supreme Court decisions are, all intents and purposes, the law of the land. While most cases are considered minor (a large number of cases are just the government arguing with itself, honestly), there are many major cases that can change people's way of life. The Supreme Court usually releases the bulk of their opinions in June, which is the most important month to pay attention to for decisions.
It's because of the Supreme Court that same-sex marriage, interracial marriage, and the right to buy contraceptives are legal, to name a few. Occasionally, the Court will overturn their own decisions, effectively undoing the protections they may offer, in an instant.
This is why it's important to pay attention to the Court: their decisions and precedents are law, and these decisions can come down quickly and without warning. The inner workings of the Court are highly secretive in that way.