[asoneth]

Of the hundreds of my students and coworkers who had both design and development skills, only a few could fill both roles on the same project without compromising on either.

But when hiring I rarely bother reaching out to them. It's not just that being responsible for both is tiring or demanding, but a project team that dedicates one person to each role delivers faster than a team with one person wearing both hats. And given that people who can do both well at the same time on the same project are exceedingly rare, they typically earn high six figures (or comparable equity) so there's not much in the way of cost savings either.

Having said that, maybe it'd be worth it for a founder or an early employee where there is a strong pressure to maintain a low headcount?

[omnimus]

On the other hand someone who can do both code and design has huge advantage of knowing where to cut corners, how to use platform features effectively and thus higher chance to make robust solution. But you need to have envinroment that allows this.

[asoneth]

Perhaps, though personally I haven't found that to be an advantage compared to having two separate roles with decent communication skills.