A BizTalk Host is a container for deployment. Several DLL's
can be placed in a single host and can be run and managed independently of
other hosts.
The thumb rule of BizTalk hosts deployment:
"Use separate BizTalk projects for your orchestrations,
maps, schemas and pipelines. Use separate BizTalk hosts to host your orchestrations
and receive locations."
Please see the diagram below for modular deployment.
Figure 3