FBCB2 is a stand alone piece of equipment that works in conjunction with a PLGR and EPLARS. The PLGR provides the positioning and the EPLARS is the data link. It is also connected to the intercom system so it can alert you if you are with in x meters of a reported enemy, but this is normally disconnected do to being extremely annoying, especially being near a minefield or something.
It is a separate component from the radios. The data link and positioning is constant, but if you want to make a spot report or cff or something you need to send the message.
In practice it is best used for navigation, as you see where you are on a map or sat picture in real time, and sending some of your daily reports like orange reports(supply status) to the PSG so he can send it to the 1SG. A lot of the other stuff it too time intensive to do in contact so your hand mic/boom mic is still the best.
IVIS used the same data link system, but was like a 486 processor compared to some hardcore gaming computer of the FBCB2