Depending on how your site is set up and how you hope to grow your community, invites may be more or less important. For instance, if your site is invite only then there is no other way to get in! Or you can create links that add people to specific groups to give them access to secure categories, or to a higher trust level the first time they log in. You can also create invite links that send the invitee straight to a specific topic.
And also you can reward people who help to grow the community by giving them badges when they invite others. Also, you can see who invited a member on their profile.
More info on how it all works is in the documentation topic: