The Reinforced variant lets you build Reactors as big as you need or want, to generate and store extreme amounts of energy.
The maximum size can be configured by players, mod pack creators or server admins in the config file of Extreme Reactors (up to 256 blocks).
Reinforced Reactors pay they superior structural integrity by being a bit more expensive to craft and not as efficient as the other variants but nothing that their superior generation capacity can't overcome.