1) Due to the designed connectivity of networks, malicious software such as viruses and Trojan Horses that may affect a single computer (from having been connected to the Internet or to a portable device) can be transferred to all of the computers on the network which will often result in an increase in costs, loss of data integrity, and possible theft of sensitive information stored on the network servers.
2) From a budgetary point of view, the initial set up, configuration, and implementation costs of a network can be high which may not be offset by the benefits of software, file, and peripheral device shareability.
3) In most cases a person with extensive training and expertise or even a team of such people must be assigned to and required to manage a network.