HLS hasn't done class rankings for a long time. The current grade system is low pass, pass, high pass. So basically A-, A and A+ got lumped together in high pass while pass lumps B and B+ and low pass = B-. I'm sure its not an exact match-up, but that's basically it. There is a mandatory curve, so the ratio of low pass, pass and high passes will be pretty constant (so unlike YLS, low passes are common at hls).
I thought it was a stupid move and still do. From students' perspective I haven't seen one iota of change in terms of competition or anything else, just a bit less transparency for grading - probably so professors can work even less hard wrt grading. Somehow they are supposedly still working out latin honors, though its not clear to me how meaningful or accurate they will be. There are also (very) few special honors given out for students at the very top of their class or section I think.
The mandatory curve will allow employers to compare transcripts, just with a bit less distinction than before. There are also other signaling mechanisms such as recommendations, law review, journals, olin fellowship and that sort of thing. Overall I think employers are less than pleased with the situation, but haven't seen anything to indicate that they are hiring any fewer hls students because of it (though a certain Justice has said he won't be hiring HLS students due to the new grading system).
The best justification for it really depends on how good the grading was under the old systems. If professors were able to meaningfully group exams by the letter grade system we had, then we've lost some transparency and that's a bad thing imho. If professors weren't able to make such fine distinctions and ended up just arbitrarily separating As from A- for example, then the new system should better reflect reality and that's a good thing.
Just my 2c. BTW my 1L year we all had letter grades. My 2L year the 1Ls only switched to L/P/H, my 3L year we were all on L/P/H.