Licences let potential users know in advance what they can do with shared data. When you are depositing data in the data repository of your choice, you can select which licence you want.
Standard licences have Terms and conditions are already defined. They might not cover very specific cases but have multiple advantages:
Examples of standard licences are
Sometimes, however research partner, funder, research institution, or data repository may require a tailor-made licence. The most common reason to adopt them is the commercial value of data. These tailor-made licences are typically written by the publisher or adapted from a standard license by adding / adaption conditions. They may increase complexity for users, and decrease interoperability.