An omni wireless antenna should only be used for local wireless networks. Generally an omni-directional antenna will evenly distribute a signal in a 360 degree radius. However, panel and waveguide(1) antennas are available to spread a signal in a 180 degree radius.
Avoid using an omni antenna for long distance links as the signal will add unnecessary interference to the surroundings due to its wide signal spread.
(1) A waveguide antenna can spread a signal in either a 180 degree or 260 degree radius. However, this depends on how the antenna has been manufactured.