It's part of the evolution of movement, you as a human being begin movement on your back, in a supine position, before having the ability to roll over. Then you begin sitting up and start crawling. Afterwards you learn to stand, walk, pick things up and carry things all before you start lifting heavier things.
From the outside looking in, it may seem like a baby will crawl as a way of transport, though it is far more than this - it's a major stage of their physical and neurological development. When coordinating a crawling movement pattern, you're using a left right reciprocal movement pattern, meaning you're improving communications between both cerebral hemispheres.
Furthermore, crawling will have the human body working against gravity, developing vestibular and proprioceptive systems. These two systems play major roles in improving/maintaining balance, whether this is a baby learning to stand, or as an older person starting to lose confidence on their feet.
In short, crawling has neurological and cognitive-development benefits. Whether you're 9 months old, 90 years old or anywhere in between - it will benefit you to have some aspect, built into your exercise program, that mimics a crawling pattern.
Below are some variations of crawling patterns that will suit a wide range of people with diverse abilities. Maybe start be adding some of these in as part of your warm up.
Variation #1 - Modified Bear Crawl - Standing
The individual may have some mobility limitations where getting into a quadruped position is not favourable. By walking with dowels, the individual will still benefit with the reciprocal gait patterning we get with crawling, without the unnecessary stress on the upper body. In addition, the individual will not have to experience the blood pressure changes people sometimes get when they get in a quadruped position.
Ensure the individual advances with the left foot at the same time as he/she advances with the right dowel and vice versa. Also, have the individual try and stay upright as possible, rather than trying to plant the dowel too far in front of the stepping foot.
Variation #2 - Bird-Dog
The bird dog is a movement that mimics the developmental pattern of crawling - almost like a static crawl. The exercise involves scapulohumeral rhythm, bracing, hip extension and rotary stability. By using a roller, as seen here, presents a good way to create a feedback loop for the individual to assess their stability throughout the movement pattern. Don't mind the wobbliness.
Variation #3 - Bear Crawl
This is a progression on the two variations preceding. It's a great crawl variation to try once you have mastered the bird dog. Try adding this to your warm up or between sets of large compound movements - i.e squats or lunges.
Again, crawling has great neurological and cognitive benefits - have fun!