Chapter 2 Advanced Routing for FortiOS 5.0 : Advanced Static Routing : Static routing tips : Always configure a default route
  
Always configure a default route
The first thing configured on a router on your network should be the default route. And where possible the default routes should point to either one or very few gateways. This makes it easier to locate and correct problems in the network. By comparison, if one router uses a second router as its gateway which uses a fourth for its gateway and so on, one failure in that chain will appear as an outage for all the devices downstream. By using one or very few addresses as gateways, if there is an outage on the network it will either be very localized or network-wide — either is easy to troubleshoot.