What is the importance of the Chestnut Tree Café (Part 3)?
Earlier in the novel Winston was at the cafe and he saw three men (Jones, Aaronson, and Rutherford) who he knew had been erased for their disloyalty to the Party. He knew because he helped to erase them from a news article that came across his desk. He was uncertain if his memory was correct, but he was fairly certain that these were the men. They were important Inner Party members who had been in league (supposedly) with Goldstein. After his experience in Room 101 Winston spends his days in the Chestnut Tree Cafe doing just what those three men had been doing, drinking Victory Gin and playing chess. In part 3 chapter 6 Winston is aware of having known them, but never allows the memory to fully emerge for fear of what might happen. He does in a sense realize, however, that this where people like him went, people who had been reconditioned and forgotten, or perhaps even erased.
He had previously seen Jones, Aaronson, and Rutherford at the Cafe just before their execution, or after their "reintegration" into society. This is similar for Winston after O Brien facilitates his reintegration back into society with torture, causing Winston to accept Big Brother, that 2+2=5.