What characterizes an end-to-end process, and why is it both the highest-value and the hardest to align?

It focuses on end-to-end integration (IT uses it for integration/regression testing; can also publish docs or discuss requirements).

It crosses functional domains and org boundaries (order-to-cash, procure-to-pay), is complex (many steps, embeds multiple modular flows), and has no single owner — so alignment costs are high. It's the highest-value, most critical scenario — document the most critical ones down to process-step level.