A strong internal community is your support system. It’s a group of people who believe in your brand, and will defend you.
Your community members can drive their own networks to your community, resulting in more customers or users.
You can call on your internal community members for feedback on your product, testimonials and ideas.
Internal communities can be built into your product in some circumstances, if your product includes a conversation platform.
Turntable.fm is a great example. People can chat within turntable.fm and so users can connect and interact with each other. When you create the right dynamic within your product, internal communities develop on their own.
Twitter is another good example. Conversations take place within the twitter platform, so internal user communities develop on their own.