There are two indispensable educational requirements for the serious student's lifelong investigation of the martial arts: The first is consistent, hands-on direction from a qualified and experienced instructor, and the second is reliable access to space appropriate to the study at hand. There is absolutely no substitute for these two components, and if either is lacking, potential declines. Unsafe and unsanitary surroundings can only speckle development with unpredictable periods of downtime, and even a dedicated and effortful plunge into the world of instructional video and martial literature will fail to raise aptitude beyond mediocrity, no matter how perspicuous or comprehensive the material, because martial skill is functionally transmitted via human interaction. That being said, significant insight may be gleaned when the serious student supplements his or her education outside the norm of structured class with independent experimentation and/or training in alternate environments.
The advantage of independent training lies the absence of distraction. It is immersion into a setting where one can explore the sequential or random permutations of form without the preoccupation of external interference. Solo, this is accomplished within a mental construct — ideas and gambits shape the mind in response to imaginary opponents or obstacles, and consequently, the body changes to adapt. It is a kind of mental-physical brainstorming that is no different than dance regulated by martial principles. The goal, then, is to test these ideas later during human interaction and study how they work. Those that do not should be tossed to the wind; those that do should be explored and refined, in order to personalize the martial art and make it one's own.
Such an exercise is obviously ideal for Internal Chinese Martial Arts like Tai Chi Chuan and Ba Gua Chang, or external striking martial arts like Karate-do or Tae Kwon Do, but it is no less useful for grappling martial arts like Judo and Jujutsu provided the practitioner keeps in mind the exercise is a study of form. Form is essentially the intentional manipulation of a body to achieve a specific goal. While it is probably impossible to learn a technique such as seoi nage without actually throwing another human being, it is not so difficult to shadow the form and speculate how the exchange might transform based on an opponent's measures to struggle or evade.
The advantage of environmental training is that it introduces external complications normally absent within the traditional martial arts school. At the dojang, Tae Kwon do students are fortunate to train on flat and even flooring; at the dojo, judoka are fortunate to grapple on soft mats devoid of gravel and asphalt. It is a fact that the game evolves dramatically when beset with precarious footing and other physical obstruction. It is not so easy for iadioka or kenjutsuka to swing a sword when ceilings are low, and students of Hsing-I Chuan may find rooting significantly less manageable upon icy roads or dry sand. One's capacity to operate in the heat and the cold are further factors to consider, in conjunction with the fact that clothing and attire will adjust to match the temperature.
Such environmental complexities should be explored, because they amplify deficiencies in the martial artist's freedom to efficiently adapt his or her form -- and that is essentially the heart of the martial arts, whether one's primary focus is self defense or self improvement. As Miyamoto Mushashi often said, "You must investigate this throughly."