Aesthetically and for their richness of flavour. Feels more sophisticated and deeper than many common plums to my part of the world, like yellow or Doris.
Their green streaks are a beautiful complement to deep purples and blood reds - their insides are also lovely and bloody often. Tart little skins, they seem to remain more taut and less watery than many and tend to have a cute and satisfying nub at the end; heart shaped and juicy. :)
if theres one thing i can't stand it's a one-dimensional ass piece of fruit. Like on that can only play on one note, has no depth in flavor. A bosc pear for example (abs hate them, worst fruit!!)
but plums are sweeet, sour, divinely juicy