why use asset bundles over resources?

So people keep saying asset bundles are the way to go, but I'm having a hard time understanding this.

So my game has a lot of terrains. If I just put them all in the build index it's a serious drawback during development as building takes forever. Building asset bundles is better. If I put my terrains into bundles I only have to rebuild if the terrains change. That's still kind of a pain.

With Resources the above issues go away. No long build times, no drawbacks at all really other then having to make sure I clean up resources I'm not using.

I get asset bundles if you need to load stuff over the network. I can't figure out why people would use them for anything else really.

So what am I missing?

 

Asset Bundles as far as i can tell, are best used to stream assets into client at game start, making the initial client size much smaller.

I was certain you didn't have to rebuild your assets every time if the object changed? Unless im wrong, check out Utomate for their automation features, and also this article:

https://unity3d.com/learn/tutorials/topics/scripting/assetbundles-and-assetbundle-manager