From the description of the enthrall spell (emphasis mine):
You weave a distracting string of words, causing creatures of your choice that you can see within range and that can hear you to make a Wisdom saving throw. [...] On a failed save, the target has disadvantage on Wisdom (Perception) checks made to perceive any creature other than you until the spell ends or until the target can no longer hear you. The spell ends if you are Incapacitated or can no longer speak.
Our group is divided on the how this should affect situations that wouldn't normally require a perception check (e.g. someone coming up to talk to the affected character). Here are the possibilities we came up with:
Things that would normally not require perception checks now do, and such rolls are made with disadvantage.
Things that would normally not require perception checks still don't.
An Internet search hasn't turned up anything on this specifically.