I've just recently gotten into reading and writing BL. I'm into all kinds of romance stories (though I've never quite wrapped my head around polygamous ones), but BL has a special place in my heart now because those stories allow for a little different type of interactions and emotions than might usually be found in a F/M romance. I feel like not having any set "gender role" to either fulfill or break frees up the relationship dynamic.
For example, in my BL romantic fantasy "The Claimed: A Clash of Copper and Gold," the MC prince is claimed as a personal slave by his enemy's son, but the power dynamics between them are unclear and continually shifting (as are the politics in the world they are in).