What should be the right time to configure Web Garden for our website(s) and the right criterion for estimating number of worker processes?

Web garden is a scenario that simultaneously running multiple asp.net worker processes on single Machine.

A web garden is utilized on a multi-core web server.

It has useful scenarios which may include when a non-CPU bound application needs to execute a long running request, such as an intensive computational request, long database transaction, or other long process. In both cases, a web garden could offer a solution by offloading the single worker process and distributing incoming requests amongst the workers in the application pool.