1. The optical illusion of plans drawn without chairs
Drawing circles on paper makes a room look twice as spacious as it is. A 180 cm table with 10 chairs really occupies a circle 2.8 m across once people lean back.
A rigorous plan always shows the real footprint of the chairs, so you can prove a waiter will slide past behind them.
2. Invisible obstacles: columns, swing doors and floor hatches
Many historic rooms and rustic venues have structural columns. Putting a round table less than 90 cm from a pillar writes off 2 of the 10 seats and condemns those guests to eating sideways.
3. The bottleneck at the kitchen pass
When 8 waiters come out at once with trays of 10 hot plates, they need a clear motorway to the centre of the room. If the first guest table is only a metre from the service door, you get an instant jam that slows the whole meal down.