Serato DJ Pro has a Quantize function which can be toggled by the above button, which is found to the right of the Display Modes drop-down.

When Quantize is enabled, Cue points & Loop In/Out points (when setting Manual Loops) will snap to your Beatgrids, as you set them.

Triggering Cue points & Reloop will also snap to your Beatgrids, so that you will never go out of time while performing.

You can select the Quantize step value that the functions above snap to, in the DJ Preferences tab of the Setup screen.

NOTE: Quantize requires Beatgrids to be enabled and set.