usually, when the soil is above the water table and some degree of cohesion or cementation is present, an excavation support is not used, in my area.
When you come across the WT, that means you've got an aquifer with possibly loose sandy or gravelly soil, that stands for 'cave-ins', so whatever support si required is used (regular slurry being the cheapest, casing being the most espensive)
Slurry may be tricky in salty water.
Another tricky situation: a pressured aquifer.
You've got a dry hole in clayey soil, self supporting, no probs whatsoever, no slurry nor casing used, until you drill a little distance above the pressured aquifer, the clay plug resistance is overcome, water almost erupts into the hole, turbulence causes caveins of the water bearing layer and the job which you believed a shoe-in is ruined.
A geologist knowing the area is always a valuable asset in these cases.