Complex sentence: External influences upon a group will have different effects depending upon which stage the group is at in its course, this has implications for how open a group is depending upon which stage of development it is at and on its strength.
Split into simpler sentences: External influences upon a group will have different effects depending upon which stage the group is at in its course. This has implications for how open a group should be depending upon the stage of development it is at, and on its strength.