The 10th Amendment is important because it restricts the amount of power that the government can hold over the entities of the United States. The 10th Amendment was especially important to the founding forefathers who penned the U.S. Constitution because they were distrusting of the majority of governmental powers.
The majority of the people who penned the Constitution were people who were Anti-Federalists. They were against the idea that the government would have full control on a society and they wanted to make sure that the nation they were setting the standards for understood this Anti-Federalism. The writers of the Constitution put the 10th Amendment into place to let present and future government officials know that they did not have complete power on society and the citizens within that society.
The 10th Amendment ensures that no government entity will take total control of the nation and that any government agency must also have another government agency behind it to help balance out the power. The 10th Amendment to the Constitution ensures that citizens and private entities get the majority of the power and control over a situation before the government is asked to step into the situation for control purposes.