Hardware

Giving individual cores the ability to boost as high as possible means that in scenarios where multi-threading doesn't scale perfectly, you can still squeeze as much as possible out of the other cores. Because the thread that bottlenecks the most can be run as fast as possible.

Or in other words: Limiting the top boost clock by 5% will effectively slow the entire CPU down by 5% as well.

That's why if you want to limit the CPU power draw, you should do it either via the power limit, or by reducing the throttling threshold. The latter can give you better performance in "race to finish" situations, where you only need a short power boost to finish a task, but it's less consistent.