WowFunctionally there is no difference between player written background and backstory from a gm perspective. Both of them will be atedious tug of war that gets worse the more into writing it the player is. For example...
Gm: this is going to be a grim dark gritty raven loft campaign.
Pc1 can I play a turtle?
Gm:yes but see grim dark raven loft
Pc1 shows up with ten pages of nonsense about how his tortle donataro is on a quest to avenge his family name after his father high king eliminated of water deep was disgraced by scheming backstabbing business partners.. oh and he wears a purple mask to match the purple grip on his quarterstaff. At every opportunity pc1 will remind someone "well on a role player and my character would.... " or try to call upon high king eliminster's name then argue with NPCs about it no matter how often the gm reminds him grim dark ravenloft so they don't exist and he was told.
Pc2 says "I'm an Everton style orc bard with cadet background. He shows up and dives into the grim dark ravenloft campaign where he discovers his character along with everyone else to fit the campaign as it progresses. . All is great.
Pc3 is also an Eberron type orc cadet bard but has four pages of msrysue fanfic about how he was wronged as a cadet and framed by corrupt superiors flto cover up their embezzling. He too says many of the same things as pc1 and never makes any attempt to join the grim dark ravenloft campaign or tie his pre written backstory to either the campaign or any other player no matter how many olive branches are extended to the party's second broken latch. Like pc1 he expects an 18 level ravenloft campaign about unethical human experimentation and the ramifications based loosely on an old racenloft module/supplement about that to significantly involve his corrupt boot camp instructors from $notbleepingravenloft
Now that is a rant if there is one.
I do not think that I could have done a similar piece so good.
Questions: Was it a hobbit teenage ninja tortle with the pirate background?
Nah sry just joking.
But I know these kind of players, especially Pc3. For them their character and its development is the most important and the top fun. They do not need superstats or crazy feets and cool magic items.
The main plot is not so important for them like their PCs emotional statistics.
They are more into whether their PC just laughs or cries or is angry at another PC or NPC because this one does not laugh or cry about whatever situation is at hand.
The upside on that: Many of them are extraordinary roleplayers.
The downside of it: As a DM you have to write a pagelong essay about your homebrew / modded official campaign world and hope that said player finds his alter ego built into that framework somewhere.
Good luck with that
I did exaggerate a bit here, but only a bit. These guys would be top of the notch players if they would try a bit to fit their RP concept to the fluff they get from the DM.
Edit: what is an everton style orc? I really feel dumb on that one.