From BitWise DocuWiki

Being detached from the server means that you are no longer connected to the BitWise server, and will not receive status updates about your contacts. You will be detached if the BitWise client is unable to contact the server over an approximately 2 minute period. Many times this is due to temporary congestion on your ISP or a blip with your connection. By default, BitWise will attempt to reconnect every couple of minutes for about 20 minutes. In most cases, you will be logged back in shortly without even realizing you were detached.

Most feature are still available while you are detached, but some feature are unavailable: