When each option makes sense
An in-house team fits when design work is continuous and growing across many surfaces, you need tight daily collaboration with engineering and product, and you're building design culture and systems as a durable advantage — typically post-product-market-fit and scaling.
Fractional support fits when you're earlier, the work is real but not yet a full team's worth, you need senior direction even to define what to hire for, you want to move before a hiring process completes, or you want to add senior leadership on top of a thin internal team.