This walkthrough from Ableton's Learn Live series shows how to record automation directly into the Arrangement View as you play. Enable the Automation Arm button, hit Play then Record, and every knob or fader move you make gets captured as a live automation curve. Press Record again to stop.
If you nudge that parameter later, your recorded automation gets overridden and the line turns grey to mark the change. Clicking Re-enable Automation instantly restores the original recorded moves.