What problem does this solve or what need does it fill?

Frustum culling is a pretty simple optimization where you put bounding volumes on your meshes and if a volume doesn't intersect the view frustum, you don't issue a draw call for that mesh. This saves a lot of vertex shader calls that would do culling on the GPU.

What alternative(s) have you considered?

This is a pretty standard feature for a renderer. I'm not aware of any better alternatives.