Varied and novel to the programmer. If you're doing the same thing day in and day out it probably isn't much use. If you're like many programmers and you're jumping between libraries and languages and platforms and APIs and domains and spheres, it's immensely helpful.
>doing mainstream, well-trodden work for which a company’s/project’s/domain’s inside knowledge isn’t needed
A core disconnect in this discussion is that many people seem to be arguing from the position of "I tried to generate whole solutions with these tools and it failed, so it's useless".
Everything is well-trodden. One of the commentators in here, who declares themselves a unique snowflake where these tools are useless, does "sockets with encryption and messaging", which is some of the most well-trodden ground in this domain. Everything is glue. Everything is a lot of relatively simple things strung together. And for all of those, portions are helped and accelerated with these tools.