Blueprints are faster to develop with in Unreal Engine, as it's quite literally built into Unreal Engine and doesn't require compiling from a separate program. It's even got live node previews to show you exactly what is being run at specific times, so it's easier to debug in too.

It really shines when you want to prototype a lot of things really fast, especially to get the game working first before the optimization step of moving functions and backend stuff over to C++.