Assets and your build

Most of the time you will import Standard Assets into your project.
The thing is you also never use them all, for example you only need one or so skyboxes and not the entire package or only one type of water instead of them all.

My question here is:
Are the unused assets also included in your build or are these left out?
I imagine it could save a fair amount of HDD memory.

Thanks for the answers, if any.

Unity automatically leaves out any assets that you do not reference in your scene. Unless its in a resources folder.

So no need to worry about excess materials and so forth being included in your build