Writing for a boss or client takes away some of the decision-making and risk, since you are going to get paid regardless of how successful the work you do ends up being. That is to say, if you write articles for a website, you are going to get paid even if the site ends up being a flop. You don't have to deal with any technical details or promotional work. You write, and you get paid. Nice and simple.
Of course, that can lead to a lot of creative stifling and loss of personal freedoms with your work. Depending on your personality, these can be a big problem.
Working for other people also means that you may end up spending a lot of your time looking for the next project, unless you are lucky enough to get full-time steady work from one client. It can be stressful to never know what your workload is going to be like in the near future, or if you are even going to have any work.
When you work for yourself, you may have to deal with a lot more than just writing but at least you know the project is going to stick around. And you get to make all the decisions and take your creativity wherever it leads you. Those are some pretty alluring things to consider.
The technical details of putting up a website are quite simple these days and you can easily do it without any real programming knowledge so that shouldn't be much of a deterrent anymore. Once created, you will have to tackle more chores than just the simple writing though. Promotion, maintenance, hosting or advertising costs, and more will have to be dealt with by you.
And of course, there is the risk. You could spend 16 hours a day writing and promoting your own site and still earn yourself nothing. A website these days is a drop in the ocean and getting an audience is hard work. Even worse, even with hard work there is no guarantee that it will pay off.
Thankfully, you can juggle both halves of the freelance equation until you come to a conclusion. Doing a little for-client work can keep a regular flow of money coming in while you plod away at building your own independent web empire. Time may start to get tight with too many things going and only then will you have to make that decision. Will you choose independence or safety?