Hi Don,
The main reason to use it is for path control of distance vector routing protocols (RIP or EIGRP). If you have two links between routers then you could use an offset-list to increase the metric of 1 prefix, making it prefer the other link.
For outbound traffic I wouldn’t use the offset-list, you can use policy based routing for this (it has more options). An offset-list might be useful for inbound traffic perhaps…for example, let’s say that you have a router with two links connected to another router that is out of your control. You could use an offset-list to increase the metric for 1 prefix so that the router on the other side prefers the other link for this particular prefix. This allows you to have “path control” even without access to the other router.
Rene