Backstories are a tricky beast. Some DMs want goodly amounts, others want none. You may run into the DM who mines your back story for "plot hooks" aka people to kill to motivate you. Or they may leave it alone completely. Your backstory may not come up in a game, or it may be a defining feature of the campaign. You never know how it will pan out so the amount of effort to put in is always up in the air.
Art from Hijinks Ensue