Intercom system is a protection system which has two goals: preventing entry of unwanted guests into a house or business place and the ability to open and close a remote gate without having to be there physically. The intercom is also used for communication needs of other sorts but ultimately within an internal network.
Unlike other security systems, whose main goal is to provide security; installing an intercom or an intercom system offers two solutions to that problem.
Intercom came on one hand to prevent the entry of unwanted people; this always a good cause. Without authorization and the actual opening of the gate or door with an intercom the guest behind a door will not be allowed entry. This gives the defense response because it prevents the entry of undesired people.
Another benefit equally important is the ability to open gates and doors without going to open them physically.
You may remember how things worked before the technology of the intercom evolved.