Of course, you can't abuse these sites by publishing garbage, or you'll soon lose your account and with it all your articles, so you need to exercise some common sense. That means at least publishing readable articles that have some usefulness to a potential real person should they come across it and decide to read it!
What is Quality Content?
When submitting an article to a submission site, it is common to use spun articles or those that are of low quality in terms of readability by a read person. While this is not what the search engines want to see in their index, its common practice nonetheless.
The chances are that search engines will not index really bad articles that are not readable by a human and their algorithms are getting ever better at spotting this kind of useless content. That means if you are relying on getting back-links to your site from articles that are of very poor quality, you may be wasting your time if they simply don't ever get indexed!
To get an article indexed and the link it contains counted by a search engine, you need to submit content that is of decent quality. By that I mean it has to be readable by a human at the very least.
Readable and Useful Content
But because search algorithms are getting so good at identifying what is and is not readable, the post is getting set higher and higher all the time. Eventually, your articles will not only need to be readable, but make good sense and be of value to a human reader in that they will gain something from spending their time reading it.
That something needs to be information, an answer to a question they were searching for (and found your article), or a solution to a problem for instance. It can be a recipe for a certain kind of cake or instructions on how to build something, fix something or buy something.
When you can produce decent quality in the content you create, chances are you are going to want to publish it on a website that you own, or as a guest post on a high traffic blog that will be of greater benefit to you than a low traffic article directory can provide.
The choice is yours!