Once you apply this setting, your iPhone will not lock automatically, and the display will remain on until you manually lock the display. While this is an acceptable setting, you will see a significant drop in battery life, as the display will have to remain on at all times, and the longer the display turns on, the more the battery gets exhausted.
If we had to recommend a setting, we would say that the auto-lock is best left at 30 seconds, as this gives you ample time to operate your device, and even if it is idle, 30 seconds hits the sweet spot.
