"I hear you" usually means that you have considered and accepted the other person's response but it doesn't necessarily mean that you agree with it. If you do not respond with a follow up response, such as " Yeah, I hear you BUT..." or "Yeah I hear what you're saying BUT..." then it is generally accepted that you agree with the other person or simply do not wish to take the discussion any further. Please contact me if you'd like to have a further discussion on the meaning behind words like these.

thank you all

If you say that, you are showing respect to the person and acknowledging that their views are important, but you are not necessarily agreeing with their opinion.

it has a feeling of sympathy and agreement attached to it, in my personal opinion. It has a deeper level of understanding than a simple "I understand".

Yes, sometimes we use this during casual conversations. Not very appropriate for formal conversations like during business settings though