Workouts are typically done in 2 dimensional space. The motions of flexing the elbows or knees (Arm or leg curls), flexing the knees, hips while extending the back (squats) are examples of sagitbtal plane / transverse axis movement. Lateral shoulder raises and leg abduction / adduction motion are performed in the frontal plane / antero-posterior axis arena. There are twisting movements that are highlighted in the transverse plane / longitudinal axis. Blah, blah, blah. To be maximally effective, exercise must incorporate modalities that utilize the aspects of each plane / axis pair in an integrated fashion. Fitness implements such as weighted bars are an excellent choice integrating the plane / axis pairs by utilizing function movement patterns.

The basic movements through the planes with free weight calls upon the body to develop strength and stability. it is important to develop stability for the body, to have a strong base from which strength can be exhibited. More important than big muscles in the arms and legs is a strong core that ties the upper and lower body segments together. For example, the split squat bicep curl encompasses strength, stabilization and core engagement. Functional actions such as bending a knee to reach down and pick something up are enhanced from the exercise. The external resistance, dumb-bell, resistance band or cable, places emphasis on core engagement and stabilization.
Surge Storm https://www.youtube.com/watch?v=H9nBHikSIkg
Enter the weighted bar. The versatility of the weighted exercise bar allows it to be utilized in a wide variety of workouts, including aerobics classes, strength and conditioning, circuit and interval classes, martial arts and kick boxing, balance and alignment, Pilates, yoga, and flexibility training. Using a weighted bar develops efficiency of movement in that everything, one’s self and the bar have to be kept from wobbling, stabilization. Dynamic Balance individuals who performed free-weight exercises (Movement with a Weighted Bar) can improve (their) balance almost twice as much as those who perform (somewhat) similar exercises on resistance-training machines. A good musculo-physiological result from using the bar is the ease of execution of compound movements. The more muscles that are simultaneously activated during a given exercise results in burning more calories.
Specifically, using a weighted bar brings a number of factors, that work on and in the body, into play. The body must maintain, while moving or at rest, a state of equilibrium. The body must be capable of accelerating / decelerating the resistance. The body must utilize ALL forces to bring the movement about. ALL forces is meant to emphasize the ground forces. Using a weighted bar is the opportune time to feel the ground as it presses back up into the body, brings about core engagement and provides a base of support for the manipulation of the source of resistance. In short, the use of the bar, coupled with various movement patterns, results in a Complete Total Body Work out.
Monoplanar workouts can make a person stronger. Specific exercises will address the targeted muscle group. Bicep curls will make stronger biceps but will not significantly impact, say, chin-ups (unless on works on / is working on their pull-up technique). Bring multi-planar activities into the exercise regimen will improve overall functionality of the body.