This is a good example of the spectrum of roster building, between quality and quantity of pitching innings. In a perfect world, you add players who give you both, but they are very expensive and if they get hurt like pitchers do, you're in significant trouble.
You also can't go too far in either direction. If you get 6 SP who you expect to be excellent for 100 innings, you will have a lot of innings funneled to your bullpen, and managing the staff in October gets dicey. If you have 5 innings eaters who go 6 innings but have mediocre results, you'll either miss the playoffs or get beaten up by good offenses in that crucible.
What Boyd appears to represent is a bet on his production over his durability. He's probably not going to exceed 5 innings much, and he may not make even 25 starts. But the plan is he's going to leave those starts in a much better place than if we had gotten Durable Joe The Innings Eater to get more outs but also give up more runs per inning. On a roster that already has several guys who you can expect to eat innings on a per start basis(Steele, Shota, Taillon), and a group of talented young pitchers who aren't ready for a full starter's workload(Brown, Horton, maybe Pearson, Assad), Boyd adds quality of innings that can combine with those other talented pitchers with durability concerns. And you pay Counsell record money to manage that balance to ensure you don't ask the bullpen to throw 30 innings a week.