Different DMs embrace different ideas about how much input their players have on the campaign where some DMs run a sandbox campaign, other than major NPCs everything that happens in the game is left to the whim of the players. Others have a more restrictive idea about how much input players should have. Some do not allow player input at all, preferring to run modules or use adventures published through LFR.
The level of player involvement is usually determined before the campaign begins. The DM gives a rough idea of what the players can expect of the campaign. My normal practice is to provide my players with an overview of the start of the campaign and the central theme. This allows them to create characters that are appropriate. It doesn’t make too much sense for a player to create an urban Ranger for a game that is going to take place 90% of the time in the Underdark.