I won't give you textbook answers to this question, for that you can just google the exact question and you will find lengthy articles and research on this subject that would definitely pop up. I'll just give you an answer based on my experience.
So the teaching certification I've gone through on Gravity Yoga, involved a practice of 12 days straight that involves hours of practice of Gravity Yoga targeting back mobility, hamstrings mobility and hips mobility. The days were alternating on specific targeted practices. That means Day 1 the focus is on the hamstrings, Day 2 focus is on the back, Day 3 focus is on the hips and so on and so forth.
And the hours of continuously practicing per day comprised of *focused - required holding the poses* :
1. 1-hour of guided (with the teacher's assistance) practice*
2. 1-hour of your sequence / teaching practice
3. 1-hour of pose modification practice
4. 1-hour of your own self-practice (unguided) practice*
5. 1.5 hours of lecture
#2 to #4 I did it on my own to add to my programme, for the simple reason that if you put it more effort and energy to something, you would gain more expertise on the subject at hand quicker.
So how do I feel at the end of the 12 days, practicing Gravity Yoga for pretty much these hours racked in on a daily basis?
Before I answer this - Imagine, practicing everyday, the practice itself involves holding poses with the intention of holding the poses for 2 to 5 minutes and each time you try to surpass your last time (meaning, day 1 my body got shocked with what I was supposed to do, to do last 1 minute was out of the question, so I barely did it for a minute, day 2 surprisingly I lasted and finished a minute, Day 3...etc). What do you think happened after 12 days?
To go straight to our fairy tale ending, I finally was able to hold the poses 5 minutes easily in terms of the practice, maybe even mid of the entire 12 days.
In terms of daily routine, I noticed that my posture is better, I prefer to squat when I sit and I do it easily, yoga poses which were unimaginable for me to do are now doable (like your hero pose or camel pose), my back craves for the correct posture so I guess I have become more mindful in lengthening my spine, I move better and more agile when playing tennis, I have more balance when doing stand up paddling, I can do the wheel pose on the Yoga Trapeze easily and somehow my body rarely makes those cracking noises when I move at an angle. The list goes on related to daily activities that we all do.
So what I am trying is, Gravity Yoga supports your other exercises (it does not replace them at all). Now when you do Gravity Yoga make sure that you do not do the exercises after. Gravity Yoga works best when you do it after your exercise. Not the other way around.
Now practically, people don't simply have the luxury of time to practice for 4 hours. A decent time spent on a daily basis for 15 minutes at the least will help your mobility. 1-hour of focused practice 2 - 3 times a week would be great.
To achieve the mobility results you want in the long-term, it can be done through regular practice.