Gunite & shotcrete retaining walls.

For anything structural, yes. What a wall is holding back, how tall it is, and the soil behind it determine the reinforcement and the drainage it needs, and above a certain height most jurisdictions require an engineered design and a permit. We build to the engineer's plan rather than to a rule of thumb.

Sprayed concrete needs formwork on one face only, so it suits curved and irregular walls that would be awkward to form conventionally, and it produces one continuous reinforced structure rather than an assembly of units. On a job where the wall and a pool shell are both being shot, it also means one crew and one pour.

It is not optional. Water building up behind a wall is one of the main reasons retaining walls fail, so drainage is part of the design rather than something added later. This matters more on the Gulf Coast than most places, because the clay holds water and the ground is flat enough that it drains slowly.

Yes, and it is common. Raised walls, elevated pool structures and the retaining work that makes a sloped lot buildable are all gunite work, and doing them with the shell means one crew and one structure rather than a handoff between trades.