One of the best uses I've found for spells that blind opponents is to pair them with a spell that also creates difficult or damaging terrain before enemies get to you. This requires two casters (since both spells require concentration) but if you can bottleneck opponents, then cast darkness and spike growth in the same area, it can be devastating. Hordes of creatures (which often have lower hit point totals) tend to push through en masse (kind of like an excited crowd trying to push through a store entrance on Black Friday) and kill off many of their number. Enemies that aren't so numerous tend to lose their sense of direction and wander around aimlessly, taking damage every round. Even if all the secondary spell does is slow movement (like grease, for instance), enemies tend to spend a while in the area and the rest of the party can pelt them with arrows or, better yet, hit them with area effect spells. Even at disadvantage, a slew of free ranged attacks are nothing to sneeze at.
This all depends on how your DM handles blindness, of course. My groups generally have enemies roll each round to see how well-oriented they are. With some bad dice rolls on the enemies' part, they might end up wandering around in the darkness until they're dead. Even if they do manage to work their way out, you can have a few PCs standing by with readied actions to shove them back in. A beefy fighter with shield master or a warlock with repelling blast work nicely.
This all depends on how your DM handles blindness, of course. My groups generally have enemies roll each round to see how well-oriented they are. With some bad dice rolls on the enemies' part, they might end up wandering around in the darkness until they're dead. Even if they do manage to work their way out, you can have a few PCs standing by with readied actions to shove them back in. A beefy fighter with shield master or a warlock with repelling blast work nicely.
