idk

All it does is that they now can start a 187 expedition on their own (which they will most likely fail if they couldn't unlock on their own)

well that depends ....

I was stuck solo on 160+ because of constant disconnections and impossible bosses ( that was before patch ) so I did 187-189 with one group

After I unlocked I can clean 187 solo ... I can't do all 3 but 187 only I can ( maybe I could even all 3 if I get lucky with bosses but it would take too much time so I do 1 only atm ....

sometimes you could stuck lower than you actually can because of that 3map progress that could f++++ you in so many ways in process ... doing 3 maps take time and often something go wrong ...

but , yes ... nothing special there ... no final boss or some benefits ....

Overall I prefer playing "Wrath of Serisel" around lvl160 = most fun and rewarding ( its not too much time consuming and you get some rewards for cleaning )

I think the benefit it simply earning higher productivity points and increasing magic find percentage.

Top tier rolls are capped at around ilvl 151, as far as I know. What I would really like to know is if EXP is increased at 187-189 vs. 80-90 expeditions.

I'm guessing if you get carried through a 187 dungeon when you are say at 79 yourself solo, it will open every level to you all at once.

Even if you can't complete a 187 on your own, the unlock enables you to farm chests in 187s at a minimum.