Here's what surprises most people: reinforcement doesn't stop concrete from cracking. Concrete shrinks as it cures and moves with the soil under it, and some cracking is normal. What steel does is hold cracks tight and keep the pieces on either side from shifting up, down, or apart.
That's the difference between a hairline you barely notice and a trip-hazard edge you mow around.
Rebar
Steel bars tied into a grid and set on plastic chairs so they sit in the middle of the slab, not on the dirt. For driveways, pads that carry vehicles, and anywhere the soil is questionable, a rebar grid is the reinforcement we trust most.
The chairs matter. Rebar lying on the ground at the bottom of the pour does very little. It has to be held up inside the concrete to work.
Wire mesh
Welded wire mesh can work for lighter slabs, but it has a well-known problem: it gets stepped on during the pour and ends up at the bottom of the slab. If it isn't supported on chairs, it's mostly just decoration.
Fiber
Synthetic or steel fibers mixed into the concrete help control small surface cracks while the slab is curing. They're a good addition, but for a residential driveway they aren't a replacement for properly placed steel.
Control joints do the rest
Joints are planned weak lines that tell the concrete where to crack. A common rule of thumb is to space them, in feet, at no more than two to three times the slab thickness in inches. For a four-inch slab, that's roughly every 8 to 12 feet.
Reinforcement plus well-placed joints is what keeps a slab looking clean for years. When you compare bids, ask what reinforcement is included, whether it sits on chairs, and where the joints will go.