Most people spend on average 1 hour in the gym, but 23 hours away from the gym on any given day. That is a lot of time to be able to undo all the good work you are putting in when you train. Remember most of your gains will come from what you do outside of gym; making sure you are eating healthy real food, getting enough sleep and rest. As I have written about before you can’t out-train a bad diet.
Additionally, if you have a major weakness such as limited flexibility or poor posture you need to work on that on a daily basis… outside of the gym. Yes, you can do mobility and stretching when you are at the gym (and I recommend you do), but for most people it won’t be enough to correct the weakness. Stretch at home or at work, sit up straight at your desk and learn how to use a foam roller and trigger point balls.
No matter what your goals are, you would benefit a lot from considering what you are doing in the other 23 hours of your day when you are outside the gym.