What are the three main disadvantages of using a computer network?

On the whole a network is a good thing to have. However, if you are not protected appropriately then I believe you may face the following disadvantages: 1. Absence of registered and secure users may leave you open to intruders who may gain access to important information on your network computers 2. Unsecured access to the Internet through your network may allow hackers and intruders to mess with your systems and as in point one, gain access to important and confidential data 3. Unless the network is set up and configured using the Star topology, one dysfunctional link may disrupt the entire network.  more

There can be as few or as many (dis)advantages as you allow there to be. It's basically dependent on exactly what type of network you're speaking of, the systems on the network, and the activities you're using these computers for.  more