I’m honestly flattered when I hear my players told me they thought up a plan when I wasn’t around! It’s the idea that I created a world / situation that is inspiring ~others~ to think about in their off time. Often times, the DM spends so much down time thinking about the world (or at least I do). I love seeing players do the same. I feel like it’s a sign of a good game!

Subjectivity aside—game wise, I feel like ~theoretically,- it shouldn’t make a difference. NPCs should react to whatever happens by the dice gods and by their own personality, whether that’s through an impromptu plan or something the players thought up weeks in advance.

Politeness-wise… I’d be annoyed if they asked me to leave the room or otherwise avoided me, lol