Unilateral training implies that it's best to train one muscle at a time. It's essentially a one-sided workout strategy in which you switch from side to side with each workout session, zeroing in on one leg.
The previously mentioned exercises can be done unilaterally to mix up your routine or provide a different workout method completely. Instead of standing on both legs or sitting and pushing with both, just do one at a time. For the straight-knee standing calf raises, this means raising your leg up and lifting your body with the strength of the other. The same goes for the seated calf raises -- just cross your legs and lift with one foot. Unilateral training is often used to work out imbalances in a person's physique and it can help balance power output if one of your calves is stronger than the other [source: Men's Health].
Ultimately, the choice between bilateral and unilateral training is yours, but both have benefits depending on the state of your muscles.