They don't make even the most convoluted anecdote any less confusing and they're cutesy nonsense. I've never called anyone "dear" in my life and I doubt most of the people here have either unless they're over 60.
Why do they persist? It just seems like a really embarassing fad that somehow stuck and has become a weird calling card of mumsnet. It literally takes seconds to type "oldest son" or "partner" instead of "DS1" or "DP" and it just sounds so much nicer and more human.
On a positive note, it does amuse me to picture everyone's family as R2D2 type robots with these little code names.