[E] High Tide can be used in a way that makes Harbor's playstyle similar to an Initiator when he's played as a second Controller. This is because Harbor has to be close to the area of the map it's used in, the ability is highly maneuverable, and it's on cooldown so it can be used several times throughout the round.
[Q] Cove is the hardest to break on pistol round. This increases the output of the ability significantly on this round, and makes using it to plant or defuse the spike much more effective.
Walking through either [C] Cascade or [E] High Tide slows enemy players. This makes it harder for enemies to contest space that your team creates and / or takes.