There are so many ways to keep yourself fit. Some are into yoga. Some are into spinning classes. Then there are those who are into running. And there others who dig crossfit. Me, I'm into weightlifting. But you know that already.
It is unfair to say that yoga is crap. Or spinning class sucks. To each his own. Having said that though, I believe that no matter what your chosen style of fitness is, you must incorporate strength training into your fitness regime. It's common sense, really.
You need to be strong first in order to excel in your chosen sport. Nobody ever benefited from being weak.
You like running? You need the muscles to give you the kind of stride and endurance that will take you further faster.
You love football? If you're a tiny prick you'll get shoved about more than you get to kick the ball.
You're into martial arts? If you want a kick that would knock the air out of your opponent you gotta be strong.
So you see, strength training is THE foundation of any kind of sport. I strongly suggest you incorporate strength training into your fitness regime regardless of what you're into.