Like the ability to hand the other person a piece of paper.
But the biggest thing that is missing is a fact of geography. Suppose we have a meeting for 6 people, and 5 are physically present. The 6th person will only be there for the official meeting. The other 5 will discuss the meeting before and after, and those discussions will set a context for and around the meeting.
No video conferencing solution can get the 6th person to participate in that unofficial activity. So unless everyone videoconferences in, the ones who do are effectively left out of a significant portion of the meeting.
Cheers,
Ben