Watch the Open G Tuning Part 1 online guitar lesson by Richard Gilewitz from Fingerscapes
These left hand positions and chords are just another sampling of locations to place your fingers as the start of your menu to choose from when creating compositions. They are very common and when learning existing pieces in this tuning you will find them helpful and eventually recognizable.
One thing I try to avoid when creating a composition is predictability and the other trap of being too derivative, either of a previous piece I have written or one that has inspired me. Sometimes very simple and subtle variations from these positions can produce some nice surprises.