As much as I frequently think it would be better if people could "really" understand everything about me, I have also started to intellectually understand that wouldn't be the best thing. For one thing, it means that they would basically have to go through everything I have gone through, and not that I think my experience is special, but I don't like the idea of anyone having gone through exactly what I have gone through. Honestly, I think it would be a pretty unhealthy relationship if someone could relate that intensely.
Although it is sometimes hard at the time when someone doesn't understand, it also forces me to acknowledge some things by saying it out loud. I don't know it would necessarily me true, but I think that someone completely understanding what I have and am experiencing may even keep me from getting better. It is very comfortable to have someone understand, and if someone understands, I may not bother trying to get better because it seems easier not to.
I have found that finding people who understand pieces of what I am experiencing helpful though. My best friend has had bad anxiety in the past, so she really knows what to do in those situations. Other people have had a shitty home life and can commiserate, and sometimes even joke about various rediculous incidents. I found that piecing it out like that can help me not feel so alone, and keeps the stress on the people around me a little lower.
In other words, I think in theory it would be great to sit down with someone who completely understood for a couple hours, but I think in thr long run in would actually prevent or prolong the healing process.