Every party needs a white mage, nobody wants to be the white mage.
I’ve been playing Genshin Impact lately and usually prefer using a DPS character, like Keqing or Tartaglia, since I like being in the middle of the fight most of the time. That said, if I join a party and see no one is a healer, I use that 30 seconds before the event starts to switch to using Barbara, one of the better healers in the game.
Her healing scales off of her HP, so a Barbara with equipment to raise HP basically makes a team immortal. Her special ability can be used every 40 seconds, but lasts for 30 of those 40, meaning it is basically on 75% of the time. It causes her basic attack to restore a small percentage of her max hp while her charged attack restores a higher percentage as health for all party members. Basically, she spams healing spells, that is her role and what she is advertised as. Considered a requirement for anyone who hasn’t been lucky enough to get the game’s best healer, Qiqi, from the gacha. Barbara is often considered boring but reliable as her attack stat is low, her outfit is a rather conservative dress in a game full of waifu-type characters and she usually wants to avoid being anywhere near the fight. Just about everyone has her as well, as she was given out for free to anyone who started the game before the 1.1 update (which is only a few weeks old, at the time of this writing, on a game that’s been out for months).
That said, in co-op, there is also another option for her to be a DPS or debuff unit. Genshin has an element reaction system where mixing different elements causes effects. Barbara is a hydro (water) element user and a “catalyst” user (spells). Catalyst users have a unique trait over other weapon types that causes her basic attacks to all have elemental charges rather than physical, so all of her attacks are water element and she can spam them from a distance, as the spells appear over the enemy rather than coming from the catalyst user themselves (except the character Ningguang, for some reason) . This inflicts enemies with the “wet” status, slowing their movement in certain events while also causing reactions to most other elements (basically, all except the plant element, which only reacts to fire). These scale off of the “elemental mastery” stat, so a specced out Barbara focused on this stat can be anything from a debuff master, DPS or supporter.
Water and fire: vaporize, causes a one time damaging hit to enemy, higher if the fire is added second. Elemental mastery raises damage
Water and electro: overcharge, causes an AoE shock to enemies every second for a few seconds, each shock has a chance to break their animations with a flinch. Initial shock has a damage boost as well. EM raises damage of all shocks.
Water and earth: crystallize, causes enemy to drop elemental particles that your party can pick up to charge their ults quicker. EM raises how much those particles restore to gauge
Water and ice: freeze, stuns enemies as they are frozen, slamming water and ice attacks resets their unfreeze timer, fire attacks break the enemy out but cause extra damage. EM extends freeze time.
Water and wind: swirl, spreading the wet status to enemies in the AoE of the wind attack.
Even if you are solo, not in a party, you can set up to 4 characters that you can switch to on the fly during battle. For a very long time (and still quite often) I like to pair Barbara and a character named Fischl as one of my better DPS team ups. Fischl is electro and her special has her summon what is basically a turret unit that spams electric attacks at the nearest enemy for a short time. She can be powered up to extend this timer, eventually having it active about 2/3 of the time. This turret acts independently of Fischl and sticks around even if you switch out to a different character. Between the turret spamming lightning and Barbara spamming water spells (bonus if you use her special to make them heal your party) the end result is a pretty decent DPS for about half the time your fighting, while 3/4 of the time you are also healing. I recently added in an ice character to go before Fischl, as ice with electric causes an effect called “super conduct” that lowers defense by 40% in an AoE on hit.