Avoid splicing motor power cables when ever possible. Ideally, motor power cables should run continuous between the drive and motor terminals. The most common reason for splicing is to incorporate high-flex cable for continuous flexing applications.
Occasionally, a technician or service person will ask me, "why not just increase the output by increasing the voltage (the current flow) to the motor?" While that may seem logical, increasing the voltage (in effect, creating an overvoltage situation) will not necessarily boost the output of the device. To understand why, you need to become familiar with a physical characteristic called "hysteresis loss."