What does writing a bio entry accomplish?
(1) IIRC from what I've gathered on the gdb, BIO entries are accessible IG via a certain magickal thing. I'll keep it that vague, but I've taken them to be extensions of my thoughts and feels for othre players to peek into.
(2) Practically, I find them useful for summarizing things up before I write a character report. I can then point staff to entries in a 'for more information, see BIO entry Whatever.' This helps keep the reports short, and it helps me keep track of what's going on better. (I usually do a:
bio add Something Amazing Happened
And then fill it in later, so I have a chronology to events, because I'm forgetful!)
(3) Spiritually (or whatever, hehe), they help me think through events in character in a less clunky way than using think and feel inside the game. I do my reports in the first person for this reason, and it sometimes allows me to sort of shake out a character's psychology and see what they really think of things, so I'm not so passive and reactionary but a bit more pro-active about events.
That's my thoughts, at least. As far as I know they are totally optional. I'm actually more of a player that plays in the moment and does improv, so I tend to really neglect them. But they can be fun!