[quote=@WilsonTurner]
[@Windicator]
The C3 is used to put all the data together, not to transmit it.

The C3 Imaging Unit receives everything that everyone in the unit is seeing, regardless of whether or not they have the C3, and then puts it together in the mech units that have the C3. You don't have to have the C3 to send the information.

It's like the thing that lets someone write a map. EVERYONE doesn't need to write a map- a couple people, maybe, but everyone else can, by default, yell out their shtuff and the one or three people that DO know how to write the map can do it.
[/quote]

Secondary benefit: Being able to relay ALL data between ALL similarly equipped (C3 upgraded) FRAMES much faster

edit:

Well, they can submit and share non-audiable map-plans without having to describe one rock different from another and hope the one guy with a map doesn't screw it up, which IRL came super-handy with M1A2 Abrams-crews when they realized their enemy was listening-in and somehow got a hold of their encryption-keys.
(OPFOR in a mil-ex is usually a dirty rotten cheating bastard by default)

Personally I'd just mount a big scope-mount, or a ground surveillance radar (active, detects motion, can potentially ID a target by how it moves), or a seismic detector (passive, same, requires everyone to stop moving).