Enemies can see your Stars on the ground before they are activated. Placing stars as bait is a great way to mind game your enemies.
Recalling your stars will create a [E] Nebula smoke for a few seconds without consuming a star. Use this to quickly cross angles or as a fake to make enemies think you crossed.
In the majority of situations, [E] Nebula should be placed so that it's flush with the entrance into the area of the map enemies are coming from. There should be no space for enemy players to lurk inside and peak from an unpredictable angle if they swing out of the smoke.