Treantmonk defined 5 out of combat roles and 4 in combat roles. 5e has tried to tease out many of their jobs (see the Healer feat and nerfing of in-combat healing).
What other jobs do you find typically needing to be fulfilled in any given party, or at least one feels a need to cover when they find it isn't covered.
Social: Either through Intimidation, Deception, Persuasion, or Enchantment someone usually needs to talk to others to get things done.
Scouting: Ambushes, layouts and traps are usually dealt with by someone with a high Dex and prof in Thief's tools and Sneak
Healing: Hit Dice only go so far. Healer/Inspiring Leader extend the working day to acceptable lengths
Utility: Scrying, Flight, Invisibility, Teleportation, Ancient Languages, Illusions, Identify, Detection, needing the thingamabob
Frontline fighter: Casters are usually weak. Someone usually stops the mooks to hold the line.
Damage: If encounters are to end in 4 rounds, the average KPR(Kills Per Round) needs to be at least 0.33, and not everybody is contributing equally. Someone often is the outlier here.
Buff/Debuff: I'm separating out Buff/Debuff from caster as more classes contribute in different ways, but this role, aggregated over the party, gets done one way or another.
Control: This usually gets done by casters that use a rich selection of spells to alter the battlefield and force choices in their favor.
Consequences of not fulfilling a given role
Social: What have you seen done when nobody is good at being Face?
Scouting: Boss rooms turn out to be a surprise. Ambushes get a surprise round. Traps deal damage.
Healing: Use a Healing Kit and Potion of Health when someone goes down. Depletion of Hit Dice simply means either the day ends sooner than convenient or you are taking the dodge action more frequently.
Utility: Casters can't have all the utility spells prepared, nor do they have the best spell. The party usually finds a way.
Frontline: Concentration is lost more frequently, squishies' HP and spell slots are depleted more quickly.
Damage: Monsters get more frontloaded actions, encounters last longer, BBEGs get to cast a 2nd spell
Buff/Debuff: Odds are turned ever so slightly not in your favor. Like a gate hinge, it adds up and the gate finds itself wide open by the end of the encounter.
Control: Just like a game of chess with only 1 player, lacking hard control puts you at the mercy of a controller either on the other end of the room, or the other end of the DM screen.
What jobs did I miss?
What other jobs do you find typically needing to be fulfilled in any given party, or at least one feels a need to cover when they find it isn't covered.
Social: Either through Intimidation, Deception, Persuasion, or Enchantment someone usually needs to talk to others to get things done.
Scouting: Ambushes, layouts and traps are usually dealt with by someone with a high Dex and prof in Thief's tools and Sneak
Healing: Hit Dice only go so far. Healer/Inspiring Leader extend the working day to acceptable lengths
Utility: Scrying, Flight, Invisibility, Teleportation, Ancient Languages, Illusions, Identify, Detection, needing the thingamabob
Frontline fighter: Casters are usually weak. Someone usually stops the mooks to hold the line.
Damage: If encounters are to end in 4 rounds, the average KPR(Kills Per Round) needs to be at least 0.33, and not everybody is contributing equally. Someone often is the outlier here.
Buff/Debuff: I'm separating out Buff/Debuff from caster as more classes contribute in different ways, but this role, aggregated over the party, gets done one way or another.
Control: This usually gets done by casters that use a rich selection of spells to alter the battlefield and force choices in their favor.
Consequences of not fulfilling a given role
Social: What have you seen done when nobody is good at being Face?
Scouting: Boss rooms turn out to be a surprise. Ambushes get a surprise round. Traps deal damage.
Healing: Use a Healing Kit and Potion of Health when someone goes down. Depletion of Hit Dice simply means either the day ends sooner than convenient or you are taking the dodge action more frequently.
Utility: Casters can't have all the utility spells prepared, nor do they have the best spell. The party usually finds a way.
Frontline: Concentration is lost more frequently, squishies' HP and spell slots are depleted more quickly.
Damage: Monsters get more frontloaded actions, encounters last longer, BBEGs get to cast a 2nd spell
Buff/Debuff: Odds are turned ever so slightly not in your favor. Like a gate hinge, it adds up and the gate finds itself wide open by the end of the encounter.
Control: Just like a game of chess with only 1 player, lacking hard control puts you at the mercy of a controller either on the other end of the room, or the other end of the DM screen.
What jobs did I miss?