Oh come ON Andy, you know me. I'm never stuck for an answer!
Quote: 'What can I do with VBA that I can't do faster with Excel?'
It's a lot more fun to go up a level or two, and treat this not as a question about "Excel" and 'VBA" as much as a question about "me at the computer" and "programming".
To which the short answer is "Decision-making".
Whether it's the user pecking away at an Excel worksheet, or Word document, or whether they are sitting at the screen double-clicking on a variety of icons, chances are strong that a Microsoft Office macro or a DOS batch file can do it faster, more accurately, and without errors.
The big thing about a programming language, IMHO, is the IF statement (and all its derivatives such as While, For etc.), which in earlier times was known as the Conditional Branch instruction.
Since my earliest introduction to computers I've loved them for their ability to eradicate the boring and repetitive past of my life, and still today that's my mantra in front of a room of users: "If it's boring and repetitive, write a macro!".
Which, at last, brings me back to the original question: "'What can I do with VBA that I can't do faster with Excel?'".
If what you are doing is repetitive and/or boring, you should write a macro (program, script etc) to do that rote stuff and free up your brain to do intelligent work, idea development; or just use the time saved to hit the golf course earlier.