This is not a good idea for a simple reason: you need the practice.

The only way to get better at writing is to write. So I strongly suggest you make an active effort to regularly find things to write about, instead of just waiting for inspiration to strike.

Now on the other hand that doesn't mean you necessarily need to publish everything you write. If it sucks, keep it in your drafts folder and maybe revisit it later.

The oft-repeated soundbite, “The only way to get better at writing is to write” certainly bears a fair amount of truth. And I definitely agree with you, inasmuch as you say that practice writing should remain unpublished until polished.

But I suggest that reading, as a complementary activity, can also improve your writing quite a bit. In fact, it's probably the case that if the sorts of people who insist on writing one vapid article per day as “practice” would write a bit less and read a bit more, they might even learn something.

In my (rather short so far) life, I’ve found for my part that where the received wisdom is to trade dignity and professionalism for practice and experience, something along the lines of the opposite tends to work pretty well. My experience is that you don’t need to “throw it all out there” and produce a large body of substandard work in order to learn to do good work (although, this certainly does work for many people). I’ve been more happy with systematic approaches, where one tries to improve skills not by public brute force, but rather by private practice, emulation, and deliberation.

In addition to the good point sgdesign made, writing helps you to generate ideas.

"I think it's far more important to write well than most people realize. Writing doesn't just communicate ideas; it generates them." -- Paul Graham, http://www.paulgraham.com/writing44.html