[Boost-users] [asio] Why are the strands in the "HTTP Server 3" example necessary?

In the HTTP Server 3 (http://tinyurl.com/yh95d2b) example of the asio documentation strands are used to synchronize the invocation of completion handlers? But why are they necessary here? As far as I get it, the handlers are invoked in strict sequential order for each distinct connection (http://tinyurl.com/ybohynd). Each connection has its own set of resources so synchronization shouldn't be necessary, should it? Thanks in advance, Boris