This is a general overview of some of the main differences between open access and subscription-based or "toll access" publications. Some of the differences can have significant effects on the impact of and access to a particular publication.
Accessibility and Citations
Accessibility is a major factor for scholarly works. Accessibility can determine how often your work is read, cited and discussed. The more accessible your work, the greater its potential impact. Access to subscription-based publications is limited by ability to pay fees, and by availability of subscriptions in particular parts of the world, whereas open access works are accessible to anyone with an internet connection.
Research suggests that open access articles are read and cited at a higher rate. See The effect of open access and downloads ('hits') on citation impact: a bibliography of studies, which discuss the fact that access barriers or lack of them determine whether research results are distributed as widely as intended.
Publication Profile and Impact Factor
Job hiring and promotions may hinge on the quality of a scholar's publications. There are many ways of assessing and measuring that quality; for monographs, especially, the profile of the publisher may be used as a proxy for the quality of the publication.More objective statistical measures, like Impact Factor and h-index, are often used to rate the profile and impact of individual articles or papers. Because the statistical measures include time-based factors, newer publications (and many open access publications are newer) take some time to show up in the statistics, and may be at a statistical disadvantage in their early years. Similarly, publications that don't take place in an established journal may not appear in traditional statistics. However, many are challenging the dominance of some of the more established statistical models of publication impact, so the development of various altmetrics is worth exploration. Impact Factor of a journal can be looked up in Journal Citation Reports and EigenFactor.
Subscription and Publication Costs
Subscription-access publications with high prices or other restrictions can only be read by those at institutions that can afford subscriptions. At one extreme, publishers set low subscription rates so as to just cover their minimized production costs. At the other, some publishers charge exorbitant prices to maximize their profit, forcing libraries to purchase publications at prohibitively high rates or not at all.
Many (but decidedly not all) open access publication cover their costs with fees paid prior to publication, often shorthanded as an "author fee" or "article processing charge" (APC). Some authors are able to write these costs into grant proposals, and many institutions (including the University of Minnesota) provide financial support for local authors to cover these fees.
Both author fees and subscription costs may be going to more than just the costs of publishing: they may support the activities of scholarly societies, offset costs of publication for authors from developing nations, and may support the profit margins of for-profit publishers. Both subscription costs and author fees can be assessed in more detail to determine value for money, which may vary among individuals and institutions.
A standard publication agreement often requires an author to transfer all copyrights to the publisher. Authors may then be unable to use any version of the article on her own webpage, deposit it in an institutional repository, or give it to students for course reading. Authors can retain some or all of these rights by choosing a publisher with an agreement granting only non-exclusive publication rights - both subscription and open access publishers sometimes allow authors to retain rights, but it is far more common in open access publishing. See MANAGING YOUR RIGHTS for more information.