I was working on WAN optimisers - ie something that would be sold to customers. With WAN optimizers you would typically put one in a branch office and one at headquarters. The boxes would then compress traffic between them. Typical compression ratios are 20x/95% - in other words your WAN link can now transfer about 20 times as much traffic. Additionally some traffic would be modified to do read ahead and write behind to provide latency improvements. An example of that was a user in Malaysia opening a Word document in San Jose, CA that was a 75kb file. Without a WAN optimiser it would take almost 3 minutes while with one it would take 5 seconds.

The problem with SSL traffic is that it is encrypted and doesn't repeat even for identical underlying data, and hence can't be compressed, nor can it be modified. This significantly hurts performance. To work well the SSL would need to be stripped off, the traffic compressed/read ahead etc, sent over the WAN and then SSL put back on. (The communication between the WAN optimisers was itself within IPSec or SSL.) SSL is designed so that you can't pull shenanigans like this, unless you have the private key of the servers, or resign the traffic with a different CA that can generate the needed certificates on the fly and are "trusted" by the user.

Many internal corporate services have moved to SSL and branch office users need to access them. Think about benefits systems, HR, documents, accounting, sales forecasting and tracking etc.

In the corporate world, it is used a lot for data loss prevention policies. It keeps employees from sending a file containing all their customers' social security numbers, addresses, and credit card to their home email account (or even one of them).