6.15For Each vs Parallel For Each

Memorize this table:

	For Each	Parallel For Each
Processing	Sequential	Concurrent
Ordering	Predictable	Completion order may vary
Downstream load	Lower	Potentially much higher
Shared-state reasoning	Easier	More difficult
Best use	Dependencies/order matters	Truly independent work

Interview phrase:

“If processing order or shared downstream state matters, I'd prefer For Each. If items are independent and latency matters, Parallel For Each can help, but I'd bound it based on downstream limits.”