Example:
You want to make a map that makes sense (volcanic close to sun or close to gas giant, and ice far out)
so...you want 3 volc, 4ice, 2 des, and 5 ast.
Make one planet group. add in volc. 3 of them. Then make the min/max closest to the star. (this means the planets will spawn close to the star.
Make another group. Asterid. 5. Make their min/max closest to the star and farthest away from the star. (theyl spawn anywhere in that stars grav feild.
make another group. ice. 4. min/max farthest away. (theyl spawn on the uotskirts)
another planet group. desert. 2. min/max somwhere in the middle (theyl spawn inbetween the star and the edge..
.....
hope this clears things up.
planet groups simply allow you to control where planets spawn and allows you to make them spwan in different places

  

So essentially I won't need to use Planet Group Contents if I use Planet Groups, correct?

Well here's the thing. To see what things would like like, I made a map with several planet groups with no planet group contents, and it looked like a normal map. Then I made a map with just one planet group and a bunch of planet group contents, and it looked the same. Can someone point out the intricate differences?

also....by default...when u create a planet group it will have 4-6 random planets in it