The mind does not differentiate between real and ‘imaginary’.
If you visualize yourself dancing, your physiology changes as if you’re really dancing.
Maybe you’ve had the experience of thinking back to something you did and not actually knowing whether you did it in waking life or in a dream.
There have been lots of studies of people practicing things mentally instead of physically. Like shooting hoops mentally opposed to physically. In most cases, both practices contribute , generally, the same amount of training. And if you think about the fact that people who practice mentally probably lose concentration and waste a lot of time… Mental exercise is probably a lot more effective than physical exercise because mentally you should perform in the best possible way, which then affects the mind to act this way. The more your mind sees you shooting perfect hoops , the more you will. Seeing it happen physically or mentally is the same thing. The mind controls your body (That’s obvious… )
Learning something new via lucid dreaming is a bit problematic because you don’t have a clear mental image of what it feels like to do it. If you’re trying for exmaple to play the guitar, then you should practice a bit first physically so you understand how it feels like etc… then by practicing in a dream, by playing the guitar in a dream perfectly, or simply mentally while being awake, you will progress.
If you try to learn acrobatics, like backflips , twists etc…
And you can do some of them but not as beautifully as you wish to do them,
if you would by any chance perform one in a dream, it would be like in real life because that’s how you expect it to be. In a non lucid dream that is.
But if you are lucid dreaming… You hit the jackpot!
You can perform several backflips over and over and have each one better than the last one. And believe me, the next day, you’ll physically do backflips that you never did prior to that. Because you built that experience.