The main uses I’ve seen for extra, light cores are redundancy against hardware failures, physical isolation, and I/O coprocessors. (Other than strictly using them for low-power operation that is.)

For redundancy like NonStop pairs or secure decomposition, the IPC must be really fast so they can work in lockstep or pipelines.

For I/O processors, the efficient one can handle interrupt processing while the performance core focuses on main application. Like in a mainframe with the hardware more condensed.

A separate socket per logical domain with its IPC overhead might not be as cost-efficient as heterogenous CPU’s. That’s also before I consider putting the new chips in existing, low-cost servers with all servers having the same chips. That might have cost and management benefits on top of it.