Sharpshooter: Every second, your critical hit chance increases 3% unless you scored a critical hit during the last second, in which case it resets to normal.
This passive is debatable- on the one hand, constantly improving your critical hit chance with a crit-fishing build is good. On the other hand, actually scoring a critical hit resets the bonus to 0%, which means you’re unlikely to see more than a 6% increase except between battles. At the same time, it can be an excellent option for a build that doesn’t do anything to improve its critical hit chances, allowing it to assure a damage boost with decently regular frequency. This can be abused in either kind of build with particular runes- like the critical rune for Impale, for an example. The best way to be sure whether or not to use this skill is to try it and then drop it, and see if you notice a difference in your damage output. If not, then don’t bother- but if it does increase your damage, then by all means go for it. Or just use it for an occasional really powerful opening blow.
Ballistics: Your damage from rockets increases by 50%.
A number of skills have ‘homing rocket’ runes for them, which is the only sort of thing this skill benefits. You’re most likely to be spouting rockets in a raw-damage build that doesn’t crit-fish or with a balanced build- other builds shouldn’t consider this skill at all. If you have a different focus, you want to turn your runes (and passive skills) in that direction, not towards adding rockets to everything. Builds that don’t want their runes for other things, though, can benefit really heavily from this skill, particularly with things like Shooting Stars or Rocket Storm at your fingertips.
As you can see, the most important thing to the majority of Demon Hunter builds is a heavy focus in either control, evasion, or raw damage output. Most of the skills reflect this- and the ones that don’t reflect this don’t so much encourage a mixed function as just plain old act strangely. There are surely uses for each and every passive skill, but keep in mind that Demon Hunter can be a very complex class to manage, and your skill selections are going to be difficult because of that. As a battlefield controller or evader, you’re going to have to always balance the utility of a skill against the raw power of another skill and make your selections very carefully. Be ready to change your choices at any moment- flexibility is very important to a class whose job is so dependent on the situation they wind up in.