Remember, Botox is a neuromodulator. It works by blocking the muscle response to nerve stimulation. Hence, animation lines in the face are diminished when Botox is injected. It is most useful for effect in the forehead, and crows feet.
Fillers, such as restylane, juvederm, and others, work by filling gaps of volume loss or the interface between falling lax tissue and the next lowest fixed point. This is typically the lid cheek interface, the nasolabial folds, marionette areas, jaw line and lips.
So these two products are mutually exclusive and can often be used in combination to help achieve a more youthful appearance.