Actions & proximity
Where controls live and how reachable they are.
Persistent UI must stay useful and unobtrusive
Persistent elements earn their place only when they serve a real, ongoing user need and stay unobtrusive — high-contrast, minimally animated, and never obscuring content or keyboard focus. A high-value control in a long form (save, submit, cancel) qualifies, because the user may be anywhere in the form when they decide to act.
Sources: NN/g — Sticky headers, Smashing — Sticky menus UX, W3C — Focus not obscured
Minimize distance to important actions
Fitts's Law: the time to reach a target depends on its size and distance — closer and larger targets are faster to acquire. The submit action belongs near the end of the form's top-down flow, kept within a glance of the user's working area rather than at the far top of the page.
Source: NN/g — Fitts's Law
Keep actions near what they affect
Users overlook actions when the controls sit too far from the objects they act on. Page-level actions belong in a page-level region that communicates "these apply to the whole form"; section-level actions belong with their section.