they are there for your use. they have some jumper pins to connect them so when they are no in use they don't use up any i/o. They are handy when you need to initialize a a new function, set the robot doing a particular function(eg. S1 could be scan room to convey data to the computer for a map and S2 might be setting the robot going.)
they are also handy when you are learning to code as you can use the to blink leds, turn a servo etc.
S1-S5 are on the analogue pin
S6 digital pin
S7 digital pin
indeed cybertooth are kinda expensive so am probably going with some L293D
indeed very expensive for 3