Facing a large group of enemy archers, I cast a spell such as Darkness or Fog Cloud which creates heavy obscurement around me and my companions.
The next turn is that of one of the enemy archers. Can they simply shoot us just as they were doing previously, with no disadvantage, because them not seeing us and us not seeing them cancels out?
I base this assessment on the following rules:
Heavily Obscured (p183, PHB):
A heavily obscured area—such as darkness, opaque fog, or dense foliage—blocks vision entirely. A creature in a heavily obscured area effectively suffers from the blinded condition (see appendix A).
The Blinded condition (p290, PHB):
A blinded creature can’t see and automatically fails any ability check that requires sight. Attack rolls against the creature have advantage, and the creature’s attack rolls have disadvantage.
Attacking a creature that can't see you or that you can't see (p193-4, PHB):
When you attack a target that you can’t see, you have disadvantage on the attack roll.
When a creature can’t see you, you have advantage on attack rolls against it.
Advantage and disadvantage cancel each other out (p173, PHB):
If circumstances cause a roll to have both advantage and disadvantage, you are considered to have neither of them, and you roll one d20. This is true even if multiple circumstances impose disadvantage and only one grants advantage or vice versa. In such a situation, you have neither advantage nor disadvantage.
Now given that my allies are now Heavily Obscured from the archers, they could take the Hide action, and if successful the archers would have to guess their position to try and shoot them (still no disadvantage, I believe). But if none of us take the Hide action, does the spell do precisely nothing in terms of making us harder to hit?