Should i have more squishy tubes?

I’m building a Specialised Diverge from a frame set that has internal cable routing.
Inside the down tube i can see a long, single hollow foam tube, yet 3 cables will be coming through the frame.

If it’s only meant to have one of these squishy tube, which cable should that be used with? The rear brake hose is the odd one out, yet this cable is less likely to make any amplified friction sounds as it does not move like the inner gear cables. Or perhaps this is something to do with Electronic gears, which I’m not running?

Any tips or advice greatly appreciated.