When training a horse, you ideally want them to be so responsive to the aids that you only need to think something and they are already responding to your subtle aids. When a horse is allowed to ignore your cues, they can become heavy and dull, causing the rider to turn to larger artificial aids such as whips, spurs and harsher bits.
In my training, I instead try to educate my horse on what the aids mean. If they ignore my aids, I will add more pressure until they start to think more responsively, at which time I will release all pressure as a reward. Incorperating questions such as the halt to trot transitions is a great way to help 'lazy' horses to think more forward, whilst also helping them get stronger in their bodies.