Whats the benefit of serving the assets by apache server or nginx over rack-cache serving the assets

Ruby
#1

I have read that $ rake assets:precompile precompiles the assets into
public folder which is easily accessible from webserver(apache or
nginx). Else the assets are served with rack-cache from within the app.
So it made me wonder what would the benefit be using one approach over
the other.

Thanks,
Uday