Any line break is sent to you blog server "as is" - as line breaks. The server is responsible for converting line breaks to HTML formatting. There is an exception for a few services that don't support line breaks conversion; in this case Flock sends fully formatted HTML.
Why don't we just send <p> tags? If we send <p> tags and ask the server to ignore line breaks, for a lot of services, it's going to store the post a big blob of HTML. That would display correctly, but wouldn't be very easy to edit: you have to track where <p> tags start and where they end.
On the other hand, if we send line breaks, the conversion to HTML can be done for display only and the post can be stored in the database with line breaks. That makes it much easier to edit if you need to fix a typo from you blog web interface. The result on the HTML served to the user is the same.
