Writing multithreaded applications increases the performance ceiling. If an application can’t take use of multiple threads, but is written in a multi-threaded way, there’s no harm done. It simply runs the multi threaded code in a single threaded way (think of ParArray) with a bit of overhead incurred for “becoming multithreaded”.

Reasoning out of adding multithreaded support for long running actions because “most systems can’t take use of the extra threads” is just irrational, especially since most modern commodity systems could have a linear improvement with the additional threads.

The single core systems are barely hurt by the memory overhead involved with provisioning CORE_NUM of worker threads. But the multi core systems can take massive advantages from it.