The Supply current can be shared by one or more resistive loads. Resistors in parallel reduce the total resistance in that network and the network in turn will draw more current. If all 3 switches are closed, the maximum current will be drawn in this circuit. If one of the switches is opened, the current will REDUCE as the resistance will be INCREASED in value.
The current in each resistor is called BRANCH current. The sum of each branch current will add together to equal the full circuit current.
The total resistance is calculated by adding together the conductances of each branch and then taking the inverse of the total conductance to make the total resistance. Parallel resistance networks are vital to understand in your study of electronics.