render()
Adding render() before a code block forces OpenSCAD to render and cache the mesh produced by that code, making each successive render much faster.

An Example
The following OpenSCAD program was a dissection of member Emmett Lalish's file Rhombic Dodecahedra Chain.
  1. Starting with the following shapes where L= the height of the module and in this case 40:
        translate ([-60,0,0])rotate([0,0,45])cube(L*[1,1,2],center=true);
        translate ([0,0,0])rotate([0,45,0])cube(L*[1,2,1],center=true);
        translate ([70,0,0])rotate([45,0,0])cube(L*[2,1,1],center=true);
        



  2. Combine each shape by using intersection(). The shape created will be just where the three shapes intersect:
    intersection(){
        rotate([0,0,45])cube(L*[1/s,1/s,2],center=true);
        rotate([0,45,0])cube(L*[s,2,s],center=true);
        rotate([45,0,0])cube(L*[2,s,s],center=true);
    }



  3. Now you want to create another form using these shapes.
    Here L is still 40, and s=fraction of the face to hollow/2+0.5
    translate([-70,0,0])rotate([0,0,45])cube(L*[1/s,1/s,2],center=true);
    translate([20,0,0])rotate([0,45,0])cube(L*[s,2,s],center=true);
    translate([100,0,0])rotate([45,0,0])cube(L*[2,s,s],center=true);



  4. Combine each shape again by using intersection(). The shape created will be just where the three shapes intersect:
    intersection(){
        rotate([0,0,45])cube(L*[1/s,1/s,2],center=true);
        rotate([0,45,0])cube(L*[s,2,s],center=true);
        rotate([45,0,0])cube(L*[2,s,s],center=true);
    }



  5. You should now have two shapes:

    The next thing to do is create a boolean difference of the second form from the first form:



  6. The next step is the continue differencing from the initial form. This time you will rotate the second form 90° on the X axis:



  7. The last step is to create another difference from the initial form. This time rotate the second form 90° on the Y axis:



  8. If you wanted to see how the form falls on the platform, you could add a cube:
    %cube([220,140,1],center=true);



  9. Rotating the form by 45° on the X axis and 90° on the Z axis will straighten the form:
    rotate([45,0,90])



  10. Now to raise the form to sit on the platform:
    rotate([45,0,90])



  11. Surround the code with
    render(){
    
    }



  12. Then put it in a module:
    module openRhom(){
       render(){
           translate([0,0,L/2])
           rotate([45,0,90])
           difference(){
              firstShape();
              secondShape();
              rotate([90,0,0])secondShape();
              rotate([0,90,0])secondShape();
           }
        }
    }



  13. Now you can quickly preview chains. Here set a variable d to be the 16.5:
    chain(20);
    module chain(n){
        translate([-(n-1)*1*d+d,0,0])
        for(i=[1:n]){
    	    translate([(i-1)*2*d,0,0])
    	    openRhom();
        }    
    }