Neither one will prevent cracks; they provide strength and a shop shouldn’t need either if you don’t have any really heavy point loading. . There are two types of concrete; the kind that has cracked and the kind that going to crack. The only way to minimize cracks is proper curing. As concrete sets, it generates a lot of heat. Controlling the heat differential between the core of the concrete and the constantly changeing ambient temperature is the key. Most people don’t bother with driveways and slabs because the thickness isn’t much. But, if you will keep it wet with burlap or something similar over the first 12-24 hours it will help tremendously. You can also have the ready mix company add ice but that’s usually for really thick pours and a skilled finisher. Pouring at night helps as well. Just do a little research on curing temperatures. And, I'll add that proper control joints help with controlling cracking.
Here's a good pedestrian explanation on curing:
https://www.thebalancesmb.com/highly-recommended-methods-to-cure-concrete-844449Agree completely.
I'll further add that you can do everything by the textbook on the actual concrete mix, controlling temps and moisture, the wire/rebar/fiber placement, the forming, the pour, joints, and the finishing---and still have cracks because of other factors going on with the grade or site prep or water impacting the slab well after the pour or a host of other things.
