Toggle Auto Input Monitoring

Use this when doing punch recording. Typically you would have it on so you can hear previous recorded input that switches to “live” at the punch-in location.

You can use the key command to toggle the mode, configure the control bar to have the Auto-Input Monitoring button available (speaker with AUTO underneath), or toggle the setting with the Record button (control-click for menu).

Turn on input monitoring for audio tracks — Logic Pro X Help

You can turn on input monitoring to monitor audio tracks that are not enabled for recording. This is useful for setting audio levels or practicing parts before you commit to recording.

Punch in and out of audio recordings in Logic Pro — Apple Support

When it comes to judging punch-in and punch-out points during punch recording, you should turn on auto input monitoring (which it is, by default). This setting allows you to hear the input signal only during the actual recording; before and afterward you’ll hear the previously recorded audio on the track. If auto input monitoring is turned off, you can always hear the input signal.