Having a symmetrical body

Practically everyone has a leg or an arm that is stronger than the other, so when you workout it's much easier to  do more reps or put more weight on your dominant arm/ leg. This often results in the weaker limb being left behind, which is not good. You'll end up being wonky and all out of proportion. Naturally you will prefer write with one hand or kick with a preferred foot, this means that you need to compensate for all that extra work the other limb doesn't do during the day. So if you are noticeably stronger with one side than another, you should get the other limb up to the same level before continuing to train your dominant arm. There's no point being able to do super heavy weights with one arm when you can't do nearly as much with the other arm.

A lot of people try to compensate for this by doing exercises that use both at once, they think that by using both arms they're working each arm in equal proportions. That is not the case, when you do an exercise that requires two limbs and one is stronger than the other, the dominant limb will take over, meaning that it takes the strain away from the weaker limb and leaving it behind. So you should actively isolate the weaker limb, this doesn't mean that you should completely ignore the dominant limb as you would be wasting the progress you've already made. For example, if your left arm is weaker than the right arm,  you should do maybe one set of bar curls and then a set of left arm only bicep curls, this way you're working both arms but putting the emphasis on the left arm in order to make it as strong as the right arm. 

If you have a limb that is weaker than the other then I strongly advise getting that limb up to scratch, not only will it make your body more symmetrical, but you will be able to go heavier/ longer in exercises that do require both limbs. 

As always, good luck