I feel like there's a lot you miss when you don't see how the person is at home or around family members. You would never see that at work because you have to keep it appropriate in front of your coworkers and managers.
I get a little annoyed when people think they know someone very well just because they work together or have worked together for years. Even if that's the case, there are so many conversations you never have and more experiences that you never have together.