There are numerous reasons why scholars choose to publish Open Access. Unlike traditional publishers and journals, Open Access has the potential to reach a wider audience and can lead to a greater research impact and higher citations rates. Furthermore, Open Access promotes collaboration with scholars across disciplines.
OA platforms and journals do not require a patron to pay to view the material. By removing fee costs on the reader, the author can reach a wider audience. More than this, readers can access research material regardless of economic status or geographical location.
Authors can deposit their scholarly work immediately into a repository. Results and research are immediately available to the great scholarly community.
As the need for OA increases, citation impacts play a role in tenure and promotions in numerous disciplines. The long term impact of OA is having higher citation rates compared to articles published in subscription journals. OA provides authors with an advantage to increase their citation rates.
OA articles are more easily located and searchable. Further, OA articles are shared more widely in comparison to subscriptions. OA articles can be placed in repositories as well, making search results higher.
OA promotes author and institution visibility more than traditional publishers and journal platforms. Because of OA fosters a collaborative environment, authors would publish OA have a high probability of having their work be more visible. If an author's work is visible, that means the supporting institution also gets more visibility. Institutions can enhance their visibility by hosting/supporting OA as well as hosting OJS (Open Journal Systems). Through linked data, funding organizations such as the NIH and NSF, who may have supported the research, also garner more web traffic
Keep in mind there is always a small fee to pay to have work published. You should always check with the journal and/or vendor about fees even if it claims to be OA. Since OA publications cost less to produce and disseminate, journals and publishers can benefit from OA.
In comparison to traditional publishing, Open Access serves the interests of several groups.
For more information, check out Peter Sauber's Open Access Overview