Use it as a situational, localized advantage field for combat
Our level 13-14 party has a paladin/sorcerer/warlock that has the ability to create and see in magical darkness, while the rest of the party has limited blindsight or truesight from various sources. This answer is based on our experiences with it.
My key message is that darkness and Truesight for several party members can be a strong situational tactic even if not all party members benefit from it (or even are somewhat hampered by it). However, it won't be the right choice for all fights.
Benefits
Party members within it are effectively invisible and therefore, as defined by the invisible condition, enjoy the following benefits, even if they are not hidden:
Attack rolls against the creature have disadvantage,
and the creature’s attack rolls have advantage.
Against opponents who lack blindsight/tremorsense/truesight/devil's sight, which is about 70% of all monsters in the MM, darkness in combination with high AC makes it very hard to hit you, and if you can see within it, a lot easier for you to hit those opponents. We had battles where a hundred opponents tried to shoot the paladin down, and failed to make much of an impact. Battles can become quite lopsided.
Because opponents cannot see you, you are also immune against many spells that require the caster to see you, or see the target point in space. And if the darkness-bearing character positions themselves well, he can also block line of sight to the rest of the party. Depending on how your DM rules the combination of normal sight, Truesight and Darkness, you also can stand in darkness and if your Truesight range is long enough to cover the darkness, you can cast or shoot out of it while enjoying these same benefits. So for the divination wizard and the hexblade, casting darkness in combat and then using these advantages works well.
Against a vampire, party members hidden in magical darkness will be able to avoid the vampire's charm attack, which in itself may already be worth it to stumble around as blind as the opposition.
Issues
The main problem of the darkness is that it blocks long-range vision to cast spells into or through it for us as much as for our opposition, so if your life cleric wants to cast healing word, on someone within, they cannot. And if your gloomstalker wants to shoot through or into it, they and their target will be invisible to each other, canceling out the advantage/disadvantage.
Because of these downsides, we found that its use is situational, and depends on the terrain and positioning of enemies. There are fights where it makes great sense, for example a 1:1 duel, or approaching enemies that have long range missile weapons over a distance, and others where it does not. It's not a simple solution for all fights that you can pull off unthinkingly -- if used in the wrong situation, blocking sight for the other two party members may do more harm than gaining protection and advantage for the two that are safe is worth.
Timing. One tactic to deal with this is time the use of darkness, depending on the initiative order. For example, we had fights where the paladin held off on casting it in their first round, to give our wizard time to set off area damage or constol spells. The team within is not deafened, so you also can coordinate with the other members when to drop it again, which is easy as its a concentration spell. (However, casting it in combat also costs an action, which is a real opportunity cost).
Cleric. For cleric, if their role is that of a tank, they could walk out in front the boundary to see out and cast spells against the opposition. Inside the darkness, the advantage/disadvantage would cancel out for them.
Gloom stalker. For the gloom stalker, if the environment is one of normal darkeness, they will be invisible anyways, and probably do best to stay outside and attack invisibly that way.
