value of co-location

I'm also curious about the value of co-location. Using a fast packet
service (Frame Relay, SMDS, or ATM) allows your on-site router to
communicate directly with a router of another ISP. There's no need to
purchase another router to place at the co-location site. Why incur the
additional cost?

To avoid having to use any of the fast packet services you mentioned?
Or to allow you to use routers, which you know about, instead of being
dependent on the random characteristics of switches the telephone
company bought?

Not using either of the last two fast packet services, in particular, will
also yield 30% more useful bandwidth from a T3 circuit. This all by itself
may make up for the co-location costs and the cost of a router.

Dennis Ferguson