Do I still need Sass for nesting?

For nesting alone, no. Native CSS nesting works in all current browsers. Sass still helps with mixins, loops, and functions.

Is the & selector always required?

Not for plain descendant selectors, but it is required for compound selectors like &.active and clearer for states like &:hover.

You can, but deep nesting raises specificity and hurts readability. Keep nesting to two or three levels.

Keep component styles together without repeating the parent class.

Nested card

Body text styled from a nested rule.

The h3 and p rules live inside the .nest-card block.

.card {
  padding: 1rem;
  h3 { margin: 0; }
  p { color: #64748b; }
}

Use & for hover, focus, and compound selectors.

Hover button

The &:hover rule is nested inside .nest-btn.

.btn {
  background: #2563eb;
  &:hover { background: #1d4ed8; }
  &.is-active { background: #7c3aed; }
}

Co-locate responsive rules with the component.

Responsive box

Padding grows at 40rem

The nested @media changes padding on wider screens.

.panel {
  padding: 1rem;
  @media (min-width: 40rem) {
    padding: 2rem;
  }
}

Do I still need Sass for nesting?: For nesting alone, no. Native CSS nesting works in all current browsers. Sass still helps with mixins, loops, and functions.
Is the & selector always required?: Not for plain descendant selectors, but it is required for compound selectors like &.active and clearer for states like &:hover.
Can I nest too deeply?: You can, but deep nesting raises specificity and hurts readability. Keep nesting to two or three levels.