No debugger in the field
A gateway deployed on a farm or a factory floor has no serial console attached. When something resets it at 3 a.m., you need the device to tell you why after the fact.
A tiny persisted black box
The firmware persists a boot count and a rolling reset-reason history to non-volatile storage. On boot it records why the last run ended — brown-out, watchdog, panic, or a clean restart — and keeps the last several entries.
That single feature has turned "it randomly rebooted" into "brown-out at boot 412, correlated with the pump relay switching" more than once. Cheap to build, invaluable in the field.