Read Brendon's post about brush based mapping
Brendon wrote a blog post about what "brush"-based mapping is and why he likes to use it. You should read it!
BSP brush mapping allows designers deep control over both level design and art. Many level designers who grew up in the 90s, when it was common to use brush-based mapping tools to mod FPSes, have a special place in their heart for this workflow.
Blendo Games has used and will continue to use brush mapping for all our 3D games. One of the huge benefits we get from it is Brendon's insane level design velocity. He can slam stuff together extremely fast, not only because these tools promote velocity, but because he's been building expertise with them since he was a child.
The other big benefit we get is that brush mapping allows Brendon to make use of his skills in both level design and art simultaneously. Brendon is both the level designer and the art director of all the levels he personally designs. We do not need separate people to handle those two roles, because he has the skills, the tools, and the workflow to do all of these things himself.
If you're new to game development, or new to level design, you might not know much about how level design workflows have changed over the last few decades. If you're curious why games seem to be costlier than ever to make, or more risk-averse than they used to be, you might be able to find some (partial) answers in the way typical development workflows have morphed to match new expectations for fidelity, scope, and scale. Over the years, "what a designer is" has changed. ("What a writer is" has also changed! Most disciplines have a similar story, really.)
Every term, I give college students at Fordham a talk about role specialization, team composition, and team size in the videogame industry. These students are usually games studies students rather than game dev students, and many of them haven't yet had the opportunity to learn about the material realities of game production. They're always blown away when I tell them how many people - or how many contract studios - are required to make your average AAA game. Unfortunately, my talk doesn't really have time to go into the history of staffing in the industry, how roles have changed over time, or what drives those changes. Maybe I should add some of this information! I think the path you can follow from tooling, to workflows, to job descriptions, all the way to typical studio staffing strategies is really interesting. Not every studio would benefit from going back to "the old ways" and expecting their level designers to also become level artists... but for certain types of games, it could make a lot of sense. It makes sense for Blendo!