The list gets pretty long, because there are obviously numerous benefits to be had if you can reduce traffic you're transmitting to remote locations. On one hand, it allows you to consolidate resources in one central data center or in larger data centers scattered across your enterprise, rather than having distributed data in all of your potential remote-office locations. As you consolidate that data, you can do so in a way that your users don't experience the lag time associated with traditional remote access. So, you get a better-performing infrastructure with consolidated data and your users in remote locations are still happy.
At the same time, you reduce your costs for WAN circuits, as you can go with either smaller circuits or you can do a lot more with your WAN circuits. If you're billed by utilization, you can reduce your costs or you can downsize your circuits.
More resources on WAN optimization
Tutorial offering WAN optimization services
Much more significant than just the cost of your WAN circuits, you get to reduce the costs of managing your data at remote locations. So, all of that overhead that you might be spending today on remote tape changes, having users or administrators forget to swap tapes at remote locations, having to replace and maintain equipment, having to worry about protecting data from walking off site or just being corrupted at remote locations, you can dispose of a lot of that hassle today.
As a result, you make your data more protected and more available at a centralized location. Even if you think your WAN infrastructure is not the best today, these appliances will make your infrastructure seem more available even with some misbehavior with your WAN infrastructure.
You can also better control your data when it's centralized and consolidated, which is becoming a big concern in compliance- and regulation-driven business environments. Overall, you will make your users happier because the challenges associated with those remote locations often result in outages, data corruption or slow response times when there is data loss. By centralizing that data, you can have a much more responsive infrastructure for your remote users.