This gist demonstrates how a generated sprite file can be optimized to shave some time off your compile.

1_slower_sprite_file.scss

@import "compass/utilities/sprites/base";

// General Sprite Defaults
// You can override them before you import this file.
$emblem-sprite-base-class: ".emblem-sprite" !default;
$emblem-sprite-dimensions: false !default;
$emblem-position: 0% !default;
$emblem-spacing: 0 !default;
$emblem-repeat: no-repeat !default;

// These variables control the generated sprite output
// You can override them selectively before you import this file.
$emblem-favorite-position: $emblem-position !default;
$emblem-favorite-spacing: $emblem-spacing !default;
$emblem-favorite-repeat: $emblem-repeat !default;
$emblem-important-position: $emblem-position !default;
$emblem-important-spacing: $emblem-spacing !default;
$emblem-important-repeat: $emblem-repeat !default;
$emblem-photos-position: $emblem-position !default;
$emblem-photos-spacing: $emblem-spacing !default;
$emblem-photos-repeat: $emblem-repeat !default;
$emblem-readonly-position: $emblem-position !default;
$emblem-readonly-spacing: $emblem-spacing !default;
$emblem-readonly-repeat: $emblem-repeat !default;
$emblem-symbolic-link-position: $emblem-position !default;
$emblem-symbolic-link-spacing: $emblem-spacing !default;
$emblem-symbolic-link-repeat: $emblem-repeat !default;
$emblem-system-position: $emblem-position !default;
$emblem-system-spacing: $emblem-spacing !default;
$emblem-system-repeat: $emblem-repeat !default;
$emblem-unreadable-position: $emblem-position !default;
$emblem-unreadable-spacing: $emblem-spacing !default;
$emblem-unreadable-repeat: $emblem-repeat !default;


$emblem-sprites: sprite-map("emblem/*.png",
  $favorite-position: $emblem-favorite-position,
  $favorite-spacing: $emblem-favorite-spacing,
  $favorite-repeat: $emblem-favorite-repeat,
  $important-position: $emblem-important-position,
  $important-spacing: $emblem-important-spacing,
  $important-repeat: $emblem-important-repeat,
  $photos-position: $emblem-photos-position,
  $photos-spacing: $emblem-photos-spacing,
  $photos-repeat: $emblem-photos-repeat,
  $readonly-position: $emblem-readonly-position,
  $readonly-spacing: $emblem-readonly-spacing,
  $readonly-repeat: $emblem-readonly-repeat,
  $symbolic-link-position: $emblem-symbolic-link-position,
  $symbolic-link-spacing: $emblem-symbolic-link-spacing,
  $symbolic-link-repeat: $emblem-symbolic-link-repeat,
  $system-position: $emblem-system-position,
  $system-spacing: $emblem-system-spacing,
  $system-repeat: $emblem-system-repeat,
  $unreadable-position: $emblem-unreadable-position,
  $unreadable-spacing: $emblem-unreadable-spacing,
  $unreadable-repeat: $emblem-unreadable-repeat);

// All sprites should extend this class
// The emblem-sprite mixin will do so for you.
#{$emblem-sprite-base-class} {
  background: $emblem-sprites no-repeat;
}

// Use this to set the dimensions of an element
// based on the size of the original image.
@mixin emblem-sprite-dimensions($name) {
  @include sprite-dimensions($emblem-sprites, $name)
}

// Move the background position to display the sprite.
@mixin emblem-sprite-position($name, $offset-x: 0, $offset-y: 0) {
  @include sprite-position($emblem-sprites, $name, $offset-x, $offset-y)
}

// Extends the sprite base class and set the background position for the desired sprite.
// It will also apply the image dimensions if $dimensions is true.
@mixin emblem-sprite($name, $dimensions: $emblem-sprite-dimensions, $offset-x: 0, $offset-y: 0) {
  @extend #{$emblem-sprite-base-class};
  @include sprite($emblem-sprites, $name, $dimensions, $offset-x, $offset-y)
}

@mixin emblem-sprites($sprite-names, $dimensions: $emblem-sprite-dimensions, $prefix: sprite-map-name($emblem-sprites)) {
  @include sprites($emblem-sprites, $sprite-names, $emblem-sprite-base-class, $dimensions, $prefix)
}

// Generates a class for each sprited image.
@mixin all-emblem-sprites($dimensions: $emblem-sprite-dimensions, $prefix: sprite-map-name($emblem-sprites)) {
  @include emblem-sprites(favorite important photos readonly symbolic-link system unreadable, $dimensions, $prefix);
}

2_slightly_faster.scss

@import "compass/utilities/sprites/base";

// General Sprite Defaults
// You can override them before you import this file.
$emblem-sprite-base-class: ".emblem-sprite" !default;
$emblem-sprite-dimensions: false !default;
$emblem-position: 0% !default;
$emblem-spacing: 0 !default;
$emblem-repeat: no-repeat !default;

$emblem-sprites: sprite-map("emblem/*.png",
  $position: $emblem-position,
  $spacing: $emblem-spacing,
  $repeat: $emblem-repeat,
  $readonly-spacing: 10px);

// All sprites should extend this class
// The emblem-sprite mixin will do so for you.
#{$emblem-sprite-base-class} {
  background: $emblem-sprites no-repeat;
}

// Use this to set the dimensions of an element
// based on the size of the original image.
@mixin emblem-sprite-dimensions($name) {
  @include sprite-dimensions($emblem-sprites, $name)
}

// Move the background position to display the sprite.
@mixin emblem-sprite-position($name, $offset-x: 0, $offset-y: 0) {
  @include sprite-position($emblem-sprites, $name, $offset-x, $offset-y)
}

// Extends the sprite base class and set the background position for the desired sprite.
// It will also apply the image dimensions if $dimensions is true.
@mixin emblem-sprite($name, $dimensions: $emblem-sprite-dimensions, $offset-x: 0, $offset-y: 0) {
  @extend #{$emblem-sprite-base-class};
  @include sprite($emblem-sprites, $name, $dimensions, $offset-x, $offset-y)
}

@mixin emblem-sprites($sprite-names, $dimensions: $emblem-sprite-dimensions, $prefix: sprite-map-name($emblem-sprites)) {
  @include sprites($emblem-sprites, $sprite-names, $emblem-sprite-base-class, $dimensions, $prefix)
}

// Generates a class for each sprited image.
@mixin all-emblem-sprites($dimensions: $emblem-sprite-dimensions, $prefix: sprite-map-name($emblem-sprites)) {
  @include emblem-sprites(favorite important photos readonly symbolic-link system unreadable, $dimensions, $prefix);
}