You can eliminate copies with the ownership modifiers but they also show you where copies are made through compiler errors if you don't use the copy operator. If you cleaned up the error messages you see where copies are necessary directly in your source code. This is a large undertaking but doesn't actually require that much knowledge about the ownership modifiers.
I also want to mention that if you have large structs you can make copies cheap (i.e. roughly just a call to swift_retain) by implementing CoW (Copy on Write) instead of eliminating copies. This will only provide benefits if the copy isn't mutated and the copy wasn't actually needed in the first place. CoW can be implemented manually but nowadays you can probably write a macro for it as well.