Monitor with headphones while field recording because you cannot otherwise hear what the microphone hears
A recorder’s bare-ear vantage gives a fundamentally different picture from what the microphone actually captures: wind noise, distant rumble, and handling sounds inaudible to the recordist in the moment will ruin the take. Wearing over-the-ear headphones throughout a session is the only reliable way to catch these problems before the take is lost — in-ear or open monitoring lets external sound bleed through and masks exactly the artefacts you are trying to detect. Because a real-world sound event has no second take, monitoring is not optional polish but the core discipline that decides whether a recording is usable at all.
Examples
A recordist in a windy park thinks the take sounds clean, but the microphone is pointing into the breeze; only headphones would have revealed the roar before the take ended.
Assessment
Explain why you cannot judge a field recording by ear alone, and why in-ear buds are a poor monitoring choice for this task.