Filler sharpens and defines the jawline. Botox into the masseter slims a heavy or square jaw, and many patients notice they clench less — plenty come for one and are glad of the other.
These two treatments target the same general area for opposite reasons: filler builds and sharpens the jawline's contour, while Botox into the masseter (the jaw-clenching muscle) reduces a heavy or square look; many patients also notice they clench less. Because they work in different directions, plenty of patients come in for one and end up doing both.
This is general education, not a treatment plan. What you actually need depends on your anatomy, muscle strength, and goals — Rocio determines that with you in person.