Yes. Even if you don't go to college now you might change your mind (or have to) later. Also, employers look to see if you finished high school not just for your grades but to see a level of commitment to finishing things, showing up long term, things like that.
Yes, high school is pretty important in my opinion. You might not be deciding now if you want to go to college, and you might not ever decide to do it. But it's best to finish high school anyway.
I mean consider this: you can go to high school and slack off whenever you want, and teachers will understand that you're a high school student and it's what you do. If you do that at a JOB, they're going to fire you right away.
I know someone who dropped out of high school, and is working a full time job with a big name company: Caterpillar. He did that through hard work and being really good at what he does, which is fixing engines and machines. There's not one day he doesn't come home with his body aching from all the work.