When I go to the gym, which hasn't been for a while, I do different things there than what I do at home. I use the gym for activities I cannot do at home, rather than repeating what I can get from a home workout. THis way the gym equipment is complementary to my home equipment and workouts, rather than a repeat of it.
I use the treadmill for running and then the weight machines for lower body, leg press, hamstrings, glutes, etc, because I can load up the weight plates and this is different from a more endurance based leg/glutes workout I get at home. I also only have access to a treadmill at the gym, so I do other forms of cardio at home and outside.
I don't do upper body at the gym because this works better at home. I prefer free weights for upper, always, so there's no need to do this at the gym. Plus, after my 2 hours' of workout with 1 hour of running and 1 of lower body weights, with core work thrown in, I'm done!
Clare