Here's a similar question: when is greased banshee better than lesmok gat?
Greased banshee deals 350 balloon, 220 armor, or 540 hull damage per clip in 3.1 seconds, but the DPS is limited by its 6 second reload. Banshee has a similar effective range to lesmok gat, is more disruptive, and is good against weak-armored high-hull ships like goldfish, spire, and squid. The fires force engis to repair slower and they're more likely to make mistakes
Here are a couple examples when greased banshee can be better than lesmok gat:
On hwatcha spire against weak armor ships. I like the combo of artemis, hwatcha, and banshee. The artemis helps the hwatcha disable at range and the banshee works with the hwatcha to break armor and kill. Burst hwatcha deals 396 armor damage per clip, and along with a banshee you're guaranteed to break armor and do hull damage. It's highly effective against fish and brawl spires who are vulnerable to disable and can absorb a lot of hull damage. The banshee succeeds by slowing down repairs and working with the hwatcha
Triple banshee junker vs double banshee and lesmok gat. Addding the third banshee gives you more disable and doesn't significantly limit your kill power. At range the three greased banshees suppress engineers and scatter fires across the ship. This can be more effective than lesmok gat which takes a while to break armor. At closer range the greased banshees can work together to target specific systems. Three banshees shooting a balloon does 1050 damage and you can balloon lock ships solely by this. Triple banshee can break most armor in one clip, and aiming at guns/engines will quickly flame out anything that's not chem sprayed. You can also stay low and use the great arcs to shoot up and use your balloon shield when there's trouble. Triple banshee isn't ideal for fast kills so the close range side of your junker should be different with either more kill power (gat) or more disable (carro)