When to use 'Support' option?

[terrypin]

Hope my screenshot clearly explains my query:

08-CoffeeLid-Cura.jpg

Q1: Is it therefore down entirely to the user to decide on that option?

Q2: I'd also appreciate feedback on my code please.

$fn=100;
translate ([0,0,6])
rotate([180,0,0]){

linear_extrude(6){
circle(d=74);
}
linear_extrude(3){
circle(d=87);
}
translate([0,0,-10])
linear_extrude(12){
    circle(d=6);
}
}
translate([0,0,13])
linear_extrude(3){
circle(d=12);
}