You might already know the answer to this question. There are lots of answers, actually, depending on you, your needs, the way the world has shaped you. Let's look at just one answer.

The easiest answer is that you might want to be memorable, and you might want to transfer your real-world reputation to the online world. A strong personal brand is a mix of reputation, trust, attention, and execution. You might want to build a brand around being helpful (what I hope my brand means to you), or being a creative thinker (e.g., Hugh Macleod) or being a deal maker (Donald Trump), or being a showman (David Lee Roth), or whatever matters most to you—and what you are capable of sustaining.

A personal brand gives you the ability to stand out in a sea of similar products. In essence, you're marketing yourself as something different than the rest of the pack. Do you need this? I don't know. Do you like to be mixed in with the pack?

What's the difference between Coke and Pepsi? There's a taste difference, for sure, but what does the brand signify? Tricky, eh? Both of those brands have spent billions so far telling us why they're different.

In some ways, the differentiator on brands is in what you deliver. What differentiates me from others might be the volume of useful content I deliver. I'm not sure. You tell me what makes me different. My answer would definitely vary from yours.

First of all, remember that branding isn't playing a role. Be yourself. It will become apparent rather quickly if you're being someone that you're not. Gary Vaynerchuk is the same guy, camera on or off. He may or may not tone himself down a bit when meeting new business partners, but I promise you that he reverts to being himself the moment someone's come to know what he's about.

Second, you may choose to use some kind of alias because you're afraid of the Internet and stalkers. That's great, except that your brand equity doesn't stretch to potential jobs, unless you go around explaining that you have a secret identity. As a guy who grew up reading comics, I'm okay with people having identities, but remember, that means the equity doesn't transfer as simply.

Finally, brands are complex, not one-dimensional. Don't try to be a one-note experience. Madonna has much more than one brand element. So does Guy Kawasaki. Don't whittle yourself down to a simple footnote. Be complex and colorful and interesting. Just be sure you can say what you're about in one easy sentence and that others have a sense of what you represent without your help. Madonna is a creative force of emotion. Guy Kawasaki is an innovator and experimenter.