I wouldn't necessarily call what I do training when alone, but I go through many techniques in my head all day long. When I get a chance I will go out in the warehouse where I work, and run through the steps and motions of techniques I like, techniques I need to work on, and techniques I may have to practice for my next test. I focus on breathing when performing kokyunage on the invisible uke, and keeping my center low when making tenkan turns. Sometimes while sitting at my desk I will go through the arm motions of certain techniques as well. The only problem with running through things like that alone are that if you are doing something "wrong" you practice it "wrong" and when you get out on the mat, it doesnt work and then you have to unlearn what you have practiced. I usually only go through technique movements solo when I feel comfortable and confident that I have my feet, legs, hips, torso, arms, hands, and head in proper position and motion. Does it work - I don't know...you'll have to ask people I train with. But yes I think it can be a good thing and beneficial if you have the foundation to build upon.