When you publish your work, it is important to think about the audience for dissimination. In other words, you should think about how your target group can access your research.
Open access is one way of providing open and free access to academic literature. The purpose of open access is to offer immediate, online access to research findings without any kind of restriction for the end user.
Depending on your target group, it can be an advantage if your research is not concealed in paid sites.