Non-essential functions

I saw on the news all these different governmental administrators explaining that a government shut down would only affect non-essential functions and that they were working on plans to operate in this way. They also said 800,000 people would be placed on furlough with the shut down. Doesn't this mean that we have 800,000 people who are government workers doing nothing important and therefore why do we have them anyway? For that matter, why do we have things in the government that are not essential anyway?