Well, times have changed, and at a dollar a bag, never do without. If you're making cocktails for more than two people, stop by the corner store for ice. Chances are, the cubes you'd make at home would be too big and stale, contaminated by forgotten freezer food. If ice cubes are more than three days old, toss them. Don't even put 'em put in your pet's water bowl.
Crushed ice chills drinks faster because more of the ice's surface is exposed.
Remember, though, crushed ice melts faster and certainly isn't appropriate for all drinks. We generally use this type of ice during the summer. Avoid using the same ice for mixing another of the same drink, and never use the same ice to mix a different drink type. Not only will you seem incredibly cheap, but you'll dilute your guests' cocktails. Although we think using ice to chill glasses is fine, don't re-use ice even for this.