Technically you never need them provided your base prep and concrete depth is sufficient. However since those two are typically unlikely or unfeasible then you use it when you need it. There has to be countless documentation on this subject.
"Designing Floor Slabs on Grade" by Anderson Ringo might have some useful insights on this - I do not remember if it goes too in depth for dynamic loading though
pavement is not a floor slab and a floor slab design manual is not recommended. suggest a pavement design manual such as Pavement Interactive. you will find everything you need for jointed plain, jointed reinforced and continuously reinforced concrete pavement design.
@StewardMMM: you may find this document useful: Link. It's pretty comprehensive.
As for your specific question: we use rebar in concrete pavement when we deem it necessary for reasons of either strength, serviceability, or durability. I know, that sounds trite. See link for more -- much more -- detail.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
Generally, we don't recommend jointed, reinforced pavement because it seldom is designed properly and ends up performing poorly. The most common jointed pavement consists of unreinforced sections 10-20 feet long that are doweled together to prevent vertical faulting. Please do not use undoweled, jointed pavement, either plain or reinforced.
The most common reinforced concrete paving is CRCP, continuously reinforced concrete pavement. In CRCP, the reinforcement provides both positive and negative flexural reinforcement, and the relatively high reinforcement ratio keeps the cracks tight and the aggregates engaged. It will crack every 3-7 feet and act as a flexible pavement. As with all pavements, it works best on a well-prepared subgrade.
The website is getting major upgrade right now, but the information is still good:
