To simGroup or to not simGroup

I am having an issue with conceptualizing what is the best way to spawn enemies. I am working on a simple top down scroller simialr to the midway games 1942, 19xx etc... I am having a hard time coming up with a good way to spawn enemies. I started with the shooter tutorial (modifying what i needed to for my uses) Now I may need to rethink my approach, the tutorial had me create enemies then randomly spawn them for some mayhem. I will need to come up with a way to spawn the enemies with more control than this tutorial covers. I have looked at the scroller demo, they seem to be spawning enemies with a "squad" system and mounting them to a wave shape but with a random element. The platformer tutorial goes through a section of using a simGroup to organize and spawn enemies. Is there a prefered way to go about spawning enemies? Also is there a resource that explains what a simGroup is and how it is used?