Authors of academic articles originally own the copyright for their work. If their article is published in a subscription journal, they usually sign a copyright transfer agreement transferring most of their rights to the publisher. It may prevent the author from putting the file in open access in a non-profit repository such as the Graduate Institute Repository, impeding the dissemination of the article and making compliance with the open access mandate of their funder complicated, from creating derivative works (such as a translation), from including portions of this work in future works or even using it for his/her teaching. For instance, PhD students who publish journal articles they wish to include later in their thesis may have lost the copyright on these articles and not have the right to use them in their thesis without their publisher's permission.
In some European countries, such as France or Germany, there is a secondary publication right allowing researchers to make the full text of their article available in open access in a non-profit repository after an embargo period if their research has been financed by public funds. There is no such right in the Swiss copyright law, which makes it particularly necessary for authors to retain some of their rights if they want to be able to self-archive.
It is strongly recommended to read the agreement before signing it and to think about the rights you may wish to keep. To make it easier for you, you can use an author addendum such as the SPARC addendum. It may, for instance, allow you to change the embargo period according to the requirements of your funder.
If you did not keep certain rights that you need, you can ask permission from your publisher.