It really depends very much upon how the company's built and how its people work culturally, but I think this is absolutely more important for larger companies

It really depends very much upon how the company's built and how its people work culturally, but I think this is absolutely more important for larger companies than smaller ones just because communication overhead far exceeds pretty much every other barrier (regulatory and compliance included). I'd hesitate to go this route if the product is aimed mostly at an audience used to structured communications such as engineers (github issues, IRC channels, and even wikis are far more structured than the usual e-mail chain like in a mailing list). This is part of why companies with usable CRM like Salesforce have done so well in providing value to their customers. So, I'd totally do this if I was going to start something that's aimed mostly at enterprise users or with potential to have a need for lots of cross-functional communication like a start-up operating in a highly regulated space.