Since the majority of the people who have been detained at Guantanamo are not guilty of anything at all except for being in the wrong place at the wrong time, the Supreme Court's decision is more a protection of the rights of the innocent than anything else.

And that is why it is important. If someone is innocent and being detained, they have a right to defend themself in a court of law. The military tribunals as they were set up by the Bush administration denied innocent detanees the ability to mount an effective defense.

The Supreme Court decision upholds the rule of law in the US. The military tribunals as set up by the Bush administration violate the rule of law in the US.