End of the day, can't most things in the real universe be broken down into a schema? Be it DNA mapping, geological data, customer invoices, product listings etc.? Everything eventually can be contained in a discrete, defined schema?
I've dabbled on and off for several years but have yet to come across one situation where NoSQL would be a better solution than SQL. As others have pointed out - as soon as you start relating table together, NoSQL starts working against you.
I acknowledge that I have 30+ years with SQL, so obviously my viewpoint is biased by what I know. Could the hesitation to adopt SQL by most new developers point to the fact that they find it too intimidating and structured?
Full-text search. Just compare the speed of ElasticSearch against "SELECT * FROM logs WHERE message LIKE '%foo%';".
Also other niches: time-series databases, graph databases, etc.
At least until you reach several hundred gigabytes, postgres uses less resources for the same search speed.
This video shows searching through 3 GB of IRC logs, filtering, ranking them based on similarity to the query, creation time, likelyhood that it’s the type of message the user wants, highlighting the part of the message with the matching words, and displaying all that:
Postgres is, for smaller amounts of data, more than fast enough.