about 4 years ago - Shurenai - Direct link
Rebar skips a step. Rebar upgrades directly into Reinforced Concrete after it dries; But for any other method you have to first let it dry once, then upgrade the concrete, then let it dry again to get reinforced concrete. Even directly crafting wet concrete only makes Concrete after it dries, and not reinforced concrete.

It's all about material expenditure and time spent upgrading. Sure, You can use wooden frames- But then you're spending a bunch of wood, a bunch of cobblestone rocks, and then a bunch of concrete not once but twice to reach reinforced concrete. On the other hand, rebar frames cost a bit of metal, and upgrade once with concrete to make reinforced concrete. One is considerably shorter, and much less stress.

Both wooden frames and rebar frames can be used to plan out a base. But one of the two is considerably less time spent upgrading, and less material used overall.. But also, iirc the rebar frames have more shape options as well, so there's that too.