Do all assets get loaded into final app from Unity development?

I truly didn't know where to look to find this answer so I apologize if it has been asked before.

When I begin to develop a new iOS app, I import a group of different assets that I MIGHT need. My question is, If I load assets into the Unity development program such as the "Standard Assets (Mobile)" and not use them at all, will they be loaded into the final iOS app when I build it? OR When I'm finished developing my app, do I need to delete all the unused assets so that they are not compiled in with the app when it's built?

I don't want my app to be huge when I build it but I like to pick and choose what assets I would like to use in the development of my app.

I hope this makes sense. Thanks so much for your help.

Tom