Document fragments are optimal for DOM updates because: 1) They provide a lightweight container for holding DOM nodes, 2) Allow batch DOM updates without live DOM overhead, 3) Reduce the number of reflow/repaint cycles, 4) Improve performance by minimizing DOM tree modifications, 5) Perfect for adding multiple elements at once, 6) Reduce browser rendering workload, 7) More memory efficient than string-based approaches, 8) Enable better garbage collection patterns.