I've been told by several friends who love React that this is one of the main selling points.
It basically just gives you a view engine and then you have the flexibility to select what other libraries you want to supplement the rest of the app components.
This differs from other frameworks like Angular where you have to "go all in" and don't have the flexibility so that if something major changes (like when the Angular team announced HUGE changes coming in 2.0) you might get stuck with something you don't like. In this way, it's easier to switch out a part of your app as opposed to having to completely rewrite something if you use a full framework like AngularJS.
I get that but there's a sort of value to a monolith that gives you most of what you'd need to build an SPA with a "guarantee" that all the components are reasonably good too.
It basically just gives you a view engine and then you have the flexibility to select what other libraries you want to supplement the rest of the app components.
This differs from other frameworks like Angular where you have to "go all in" and don't have the flexibility so that if something major changes (like when the Angular team announced HUGE changes coming in 2.0) you might get stuck with something you don't like. In this way, it's easier to switch out a part of your app as opposed to having to completely rewrite something if you use a full framework like AngularJS.