I think that software made for one fills a similar niche to ultra-processed foods — many of which were created to supply soldiers with sustenance in an active war, and continue to fulfill the needs of their consumers (travelers — who might not have the time or space to practically prepare a home-cooked meal, working professionals — who similarly benefit from less planning and food preparation), but as research has evolved, society has realized that these meals are linked with metabolic disease and adverse health outcomes.

Applications for one, might serve as a sort of "ultra-processed software" that can fill useful niches like generating textbooks on the fly (https://news.ycombinator.com/item?id=48130679), generating focus oriented music for long study sessions, and obviate writer's block.

However, I feel like there are downsides that are both obvious (insularity, discoverability, reliability, and platform dependance) and non-obvious issues which will take time for the public to determine what they are.