There is a benefit to meeting which doesn't come from the answers to your questions - (btw I asked about name, the birth, BM's hobbies, any memories or anecdotes about DD she would like to share and have DD know about, the things she hoped for DD's future, which of her birth relatives DD most takes after, what she wanted DD to know and be told about her, what she most wanted to hear about in letterbox, among other things)
That other benefits are that you've only heard about BM on paper so far, and this is quite abstract. Meeting her, and seeing and interacting with her as a human being, adds a whole new layer to this.
I heard all about lack of care, abuse etc, and I was really apprehensive before the meeting for these meetings. But I found that I gained a lot of empathy for her, and I gained even more insight into why she was never going to be able to change. I can't really state how much I gained from seeing her, from knowing her a bit, as a human being, not a figure on paper. There are some things that can't really be conveyed in writing
I also picked up on some of her mannerisms that DD also has, which I have been able to share with DD, and DD loved hearing that.
You can tell your child some things about their birth parents which are not second hand from a social worker, but that comes straight from you. Paperwork which says "X loves very much" is not the same as, "I met your birth mum X, and she told me that she loved you". I know this, because your birth mum told me so herself, rather than I know this because a social worker told me. I can tell you this about your birth mum from my experience. I think that's very valuable
I really think meeting is very worth it in a lot of situations (though obviously not all). I met even though there was a history of serious neglect and abuse, and I personally feel that I gained a huge amount and the meeting was very helpful to me. Indirectly it's been beneficial to DD. Also, the fact that BM met me, is more evidence that she was in many ways accepting the adoption, and that's something that's helped DD.