That’s a little unkind… bonita’s awesome documentation is of no help though I do understand… 
sometimes.
Parallel just means they will be sent out at the same time, Sequential means the first must be completed before the second, the second must be completed before the third etc.
To answer your first question have I used it Yes, But only with Calling subprocesses. I’ve never used it explicitly for a human task, though I do see a possible reason as to why I would.
The creation of the instances of the process is left to Bonita itself. All you have to do is decide, for
Create a defined number of instances = integer 5, or 10 , or 100 at a time. Basically a Constant.
whereas
Create instances from a list is for example a variable number of iterations.
List myIList = [A, B, C, T, V]; // 5 iterations or
List myIList = [A, B, C, T, V, X, Y, Z]; //8 iterations
with myIterator = A, then B, then C…
Note: my LIST is String and is not based on numeric. It will simply work on myIList.count() items.
This thing about the List and the subprocess method is you can send your myIterator to the subprocess if you have mapped the variable between the two.
For example, I have:
List<List> = [[name, street1, street2, town, postcode], [name, street1, street2, town, postcode], [name, street1, street2, town, postcode]]
if myIterator is List then I can send it to a (e)Mail processor to send/print a form letter to all the people in the list.
Believe me it works
What is the limit on the list or the defined list - don’t know, but I could certainly imagine a list of 1,000; 10,000, 100,000 being processed if not careful.
Hope this helps,
regards
Seán