Sorry, I will try and be more clear there are some good descriptions of this technique on the web but I can't remember what it's called. Still you have the basic idea and it's downsides. Still normally your dealing with larger objects so the overhead is a little different.

Just think about how a you normally work with objects. Normally you have a pointer to some allocated memory locationObjectPointer = (x00100) which points to a chunk of memory the size of 3 floats (x,y,z). Now normally when you update x and y you overwrite their memory locations which is fast in single threaded programming but you need to worry about something reading after you update x at (x00100) but before you update y (x00104).

However, if instead of updating in that memory block you created a new object locationObjectPointer2 = (x00600) copy'd what was in the original object and then when your done changed the pointer from the old object to your new one. Well, as you say you have the overhead of keeping track of references or doing garbage collection, but at the same time you can do a vary fast lock when you want to change the pointer and test to see if the object was changed. That test is actually hard to do with most types of memory management systems and normally creates a lot of overhead so it's a trade off.