6.50The distinctions you absolutely need to know

map vs For Each

map:
transform data

For Each:
perform processing/side effects per item

For Each vs Parallel For Each

For Each:
sequential

Parallel For Each:
concurrent

Parallel For Each vs Scatter-Gather

Parallel For Each:
same processing over many items

Scatter-Gather:
different processing routes over same event

Flow Reference vs async messaging

Flow Reference:
synchronous function-like call

Queue/event:
asynchronous handoff