A tiled shower can have hundreds of feet of grout lines, and grout is where soap scum, mildew, and discoloration start. A slab shower replaces most of that with a few large panels, often one per wall, so there are only a handful of sealed joints to wipe down.
The look is different too. With full-height panels, the stone's veining runs uninterrupted from floor to ceiling. Where a wall meets a bench or a niche, the edges can be mitered so the pattern appears to flow over the corner, which is where the 'waterfall' name comes from.
Slab walls go on after the shower is framed and waterproofed, and they're templated like a countertop: every panel, valve opening, and niche is measured from the real walls. That means your plumber and your fabricator need to be on the same schedule, and your fixtures need to be chosen before templating.
Material choice matters in a wet space. Quartz is non-porous and very low maintenance. Marble is beautiful but needs sealing and gentle cleaners. Granite sits in between. Whatever you choose, ask how the joints will be sealed, how the curb and threshold will be finished, and which pieces will be cut from the same slab so the color matches.