A discipline specific repository collects data within a specific research domain. Focusing on a particular topic allows a repository to offer more targeted support for submitters, such as supporting unusual file types, providing metadata fields that address specifics of the domain, and offering other specialized services such as visualizations. 

For instance, the Protein Data Bank, or PDB, is a discipline specific repository that collects protein structures. It provides 3D structure models, metadata that address macromolecule content and other domain relevant information, and supports mmCIF files. These elements may not be supported in generalist repositories, and offer submitters ways to better enrich and more accurately describe the data they deposit. 

In general, research data management standards advise to submit to a discipline specific repository when possible. You can read more about discipline specific repositories, what they offer researchers, and why submitting to one is a good choice for your data, here.