I like reading bios, whether it's an agent's, author's, or anyone else's. It seems to me an introduction, a substitute for the first impression you'd be able to get of someone if you could briefly meet them in person.
One thing I've noticed repeatedly and that does annoy me though (as a general impression, not especially having to do with literary agencies) is how often women's bios tend to include the personal information and men's do not. It makes me feel like oh, I get it, women are really all housewives who do a lil business on the side whereas men are too important and serious with their business to bother mentioning their family and interests. So to me, that backfires and I read it as such men being arrogant and self-important. Which would probably surprise them lol.