Welll I think some women are picky about their ring because they'll wear it for the rest of their life. You want to get a style, cut and setting that you like.
As for the purpose, well, to me its a silent marker or love/commitment. Like a friendship bracelet or something. I'm sure there's some historical stuff to back it up but that's what it is to me.
And I think if a guy ever had a girl want to trade up for a bigger ring, he should take it back for good. Sounds a little too much like an early stage of Bridezilla.
