I can use the parts, but the crafted gear earns more points that the components to craft it. For example, the Mk3 Holo Projector Salvage can be used for Aurodium Heatsinks. They award 10 points per holo projector salvage, but award 500 points for the crafted holo projector. It takes 20 of the salvage to craft the projector, so if you just use the salvage parts, you come up way short compared to using crafted gear.
It takes 20 of the Mk3 Holo Projector Salvage to craft the Mk3 Holo Projector. The math works out this way:
Points for crafted Mk3 Holo Projector = 500 points
Points for 20 Mk3 Holo Projector Salvage = 200 points
This is just an example (I have no shortage of need for the Holo Projectors). But there are plenty of other situations like this with lower-level gear that isn't needed by many characters.