ESB is a term with many definitions. There are some common capabilities described within the varied definitions but generally a specific defintion will depend upon to whom you’re talking. You can be sure, however, that when SoftwareAG says “ESB” that it means something different than when TIBCO says it. Or Oracle. Or SONIC.
It is not a framework. For SoftwareAG, it is simply a new label on tools they’ve had for a long time. That’s actually true for most products labelled as ESB–it is simply a new label.
The benefits of an ESB are the same as they’ve always been for middleware tools.
Search the web for ESB. You’ll find more than enough material to answer your questions.