If your lover is const
ant, and you want to do everything possible to keep from changing her, you must pass her by value.
However, if your lover is very large, larger than you can easily lift, you will probably prefer to just get her reference, and go to her, rather than bring her to you.
If you are forced to share your lover with others, then you will need to have her passed to you by reference. But be sure to leave a sign on the door to prevent unwanted interruptions.
Also, I learned the hard way today that while it may be useful to pass in a lover by reference, it is a very bad idea to return her by reference (If you have declared her your one and only), as others may sully her before your recipient has a chance to.