Unused pins (I/O pins) of bus switches and analog switches can be left open. The control pin needs pull-up/pull-down.
It is recommended, however, to pull up or down the I/O pins that are exposed to large external noise or other disturbances. In this case, the pull-up and pull-down resistors on the input and output sides of a switch should have the same value to make their voltages equal in order to prevent unnecessary current flow.
The following documents also contain related information.