You are asking two different questions "helpful for" is way different than "a good business for..".
Do you need to learn stuff, to gain experience OR you have some experience and you'd like to focus on the stock market, to create a business?
It depends how do you want to sell.
1. Do you want to sell on some professional website, to make some real money
2. Create your own website and (try to) start selling.
For 1 there are severe criteria to post. Most of the old and good websites (no advertising, I just like: iStockPhoto and Corbis) will accept you only if you have quality pictures. Quality does not only mean "without-noise", "well-focused", "sharp". No. It's also about creativity and your experience as a photographer. In my opinion, in stock photography you need to think as a designer and imagine how can you use a picture, in what domain, what impact will it have on the end-user and many others. Now, to create quality photos of interesting things, it's the hardest challenge. You need quality lenses, lights, a great camera and maybe a studio - in one word: lots of money to invest. It's hard to take quality pictures with a beginner camera. Not impossible.
For 2 you can post your own photos but, from this point to selling and making money, there is a long way. Nowadays it's almost impossible (just my opinion) to create a successful business by your own from stock photography. There are many factors like: quality and low prices, a creative website and the most important, the marketing and the way you promote.
A great interview maybe will help you more than this entire post