Thanks, makes sense for the brake booster.
Although I'm still wondering why the fuel regulator/filter vacuum hose is connected to the F-shaped joint (support) which is before the throttle. I actually tested it by disconnecting it from the F-joint and connecting a syringe to it. Increasing the air pressure also increases the fuel pressure.
But the location (before the throttle) makes me wonder if the air pressure variations at that point affect it substantially to make a difference, compared to putting it in the intake manifold after the throttle where the pressures are very different between idle and WOT.