@Buka , to answer your question it is primarily/mainly for the knowledge and experience. I'm probably one of the few people on this forum who doesn't train for self defense but instead train strictly as a lifestyle choice.
HOWEVER, as someone who is getting older and realizing the possibility of having to physically fight someone in an actual situation I am curious about the philosophies and principles of certain arts (like the ones that I have inquired about) and how they generate power without relying to much on muscular force, their respective ideas on footwork, movement and using an antagonist's own momentum against himself, etc.
And as far as Tai Chi is concerned I intend to eventually study that and practice it for it's own merits for the remainder of my years on earth.
Take Care and Have A Great Day,
Osu.