I find this is very game dependent but as a rule of thumb I subscribe to the idea that character creation is play, so best done together as a group.
I tend to come to a game with some high concepts that I might find interesting to explore but I hold off and keep it vague and only make the decision which concept to go for through the conversation with the group.
Ideally I want input from other players (and gm)—like mentioned in the other thread about what makes a good player: being a fan of the other player characters! And this is much easier if we share and collaborate and are not “precious with our toys” but invite others to invest in them, as well!
To come back to how this is dependent on the game: if we play Apocalypse World (or most PbtA), we are meant to slip into scenes in the session in which we also create our characters, so a lot is vague and will be found out in play.
Then, in Forged in the Dark games it’s actually super important to just start with a very rough concept? There are so many mechanics in that game that are about, even as a player, discovering things you did not know about your character. It’s a huge part of the fun of those games, I feel.
While when we start a campaign of Burning Wheel that’s going to go 20-30 sessions, the involved character and world creation means two sessions of 3h each can be completely justified… and need to be done together, even if we at times are each pouring over the book and flipping back and forth.
Regarding streaming: Yes, I absolutely find value in watching character creation live! Here is a secret, when I watch an Actual Play, I am not just watching these characters go on a journey through the fiction; I am also watching the players go through an arc.
If character creation is completely withheld, I miss out on an important part of that and I think it is an important quality of APs to let the viewer take part in the play, not just the performance.