there are two big arguments for a denser layout, notably you move your hands less, which means you can type faster, statistically speaking. It makes it easier. Generally you see typing speed track roughly with this over time.

And since you move your hands less, it's ergonomically better for typing, so you get less strain, you have better ergonomics in general, you can type longer, and even faster since there is less strain.

Different layouts optimize for different things, some optimize for efficient roll combinations, some optimize for switching between hands as optimally as possible. Some don't really do any of that (qwerty) which also have a significant impact on typing.