Loop vs Cron
A cycle that can pace itself, versus a trigger that only ever fires on a fixed clock
Loop
Can be self-paced: the agent decides when the next iteration should run based on what it actually finds, checking again sooner if something looks urgent, later if nothing has moved.
Cron
Always fixed-interval: a scheduled trigger fires on a clock, every five minutes, every morning, regardless of whether anything has changed or whether now is genuinely the right moment to run again.
Which one do you actually need
Cron is one specific way to drive a loop, the fixed-interval way. A loop doesn't require cron at all, it can pace its own next run based on progress instead of a clock. Reach for cron when the right cadence is genuinely fixed and known ahead of time, reach for a self-paced loop when the right moment to check again actually depends on what the work itself turns up.