By "generous hitboxes" I mean making it easier for the player to dodge enemies (which can be a combination of size and precision). For example, if the player and enemy sprites were circles, I would have the hitboxes be a few pixels smaller in diameter than the sprite itself. That way there's a little wiggle room for the player, and the sprites have to really overlap for a collision to occur.
Sometimes if the hitbox covers more area than the sprite (whether it's too big or a different shape), or even is the same size, the collision can feel a little jarring, sudden, or unfair. Even if it technically is fair (eg: hitbox is exactly same shape and size as the sprite).
