When attacking, it's important to have an unit comp that includes proper turret fodders.
For example, high DPS (damage per second) units are typically your Heroes and Tanks. These units can single handedly wipe out and entire base if left alone to roam an enemy base. However, a defense comprised of Rocket Turrets can often 2 shot a tank, taking it out in a matter of seconds. Likewise, the tank can destroy rocket turrets in just a few shots as well.
Therefore, if you can divert a few volleys of a rocket canon's fire, your tanks will be able to destroy the rocket turrets before taking any damage. Fortunately, once a turret locks on to a target, it keep shooting the same target until the target is destroyed or itself is destroyed. Therefore, if you lay down the turret fodders into combat first, then quickly sending in your high DPS units after it, you can often destroy a whole pod of turrets before taking any damage.
For Rebels, Wookies make great turret fodders for the Han Solo. Because Han Solo runs much faster than Wookie, be sure to have several Wookies ready to be deployed one at a time to distract each turret before Han Solo gets in range.
For Empire, an army of Dark Troopers make for great fodders. And sending them in before deploying a couple of tanks and/or Heroes can often give you the advantage you need to take out the entire base.
Definition of fodder on wikipedia:http://en.wikipedia.org/wiki/Cannon_fodder