Visiting someone else's place is great. You eat their food, drink their imbibables, and meet their guests.
But eventually to host a gathering at your own place takes hold. You want to choose the hors d'oeuvres, cue up the playlist and invite your own friends -- in your own home.
It's no different with blogging. True, your organization can go quite a ways in engaging the online world by commenting on third-party blogs. But if you want to be serious about joining the conversation, you'll want a place of your own: an online home for the conversations you want to have.
And while you have no more control over where those conversations ultimately lead and what other conversations may start than you do when you're hosting a party, you're the one who sets the agenda. And it's your voice that sets the tone and pace for your audience.