I understand that there are many ways to design a solution. When we should use a

When we should use an asynchronous vs synchronous processes, is explained with an example in below link.
If you have missed this forum.appian.com/.../Using_a_Sub-Process.html
The important point here is: We have to use synchronous sub process, when we need sub process activity (or sub process variables) in parent process.
If parent process activity and sub process activity independent of each other, then both these processes follow asynchronous relation.

When we should use an asynchronous vs synchronous processes, is explained with an example in below link.
If you have missed this forum.appian.com/.../Using_a_Sub-Process.html
The important point here is: We have to use synchronous sub process, when we need sub process activity (or sub process variables) in parent process.
If parent process activity and sub process activity independent of each other, then both these processes follow asynchronous relation.