The Rule
Don't substitute vagueness for depth
Authors use "seemed," "appeared," and similar vague constructions to imply mystery or depth where the really isn't any. "I'm afraid to commit," this phrasing says. There is probably an element of limited POV that encourages this: "The narrator doesn't know whether this is so or not, so it seemed that way to him."
Don't be vague unless there's a payoff.
Counter-Example
The coach wobbled slightly and Arabella, seeming to lose her balance dropped her purse to the ground with a clatter, and the snakes receded into the shadows.
- Donald Scott Strong, "Lair of the White Worm"
A legitimate use of "seeming to" because Arabella's nature is a primary question of the story: Is she a shapeshifting antediluvian reptile? Or is she just a klutzy woman?
Commentary
E-mail from @Meredith in episode 8's mail segment references an interview with Stanley Kubrick, where he mentions H. P. Lovecraft's admonishment to not explain things. (If you can get the effect you want in the reader without an explanation, don't do it.)
Ready Player One phrase counts: