features: what does it do?
Allows efficient, intuitive and on by default quick navigation across settings pages with frequently changing and impossible to remember layout.

why do we need it?
For the same reasons we had it all along. This is by far the fastest way to navigate settings UI. Recent examples:
- Smart lock feature was added. Opening settings and typing "lo" (lock) highlights it and reduces the page content to manageable. Cost to the user: Two key presses.
- Even better: typing "sm" (smart) brings the button in view and highlights it. Cost to the user: 2 key presses and some memory.
- Enabling Android apps. Open settings UI and type "Android" (or probably some fraction of it). The requested checkbox appears and is scrolled into view. Cost - typing a word.

No real replacement I can think of in the current UI other than using Chrome find in page search. While possible to find controls above the fold most settings are hidden behind Advanced and thus not searchable like that.

It is also a big step back for accessibility users.

I hope the search is coming back.