Authors get an easy-to-setup environment to work on their paper.
Inline hints help the create the proper structure.
The "as-you-type" validation removes the anxiety of submitting a paper that does not respect the conference constraints.
Also by integrating a reporting service, the validation errors can be centralized and tracked in case the authors cannot fix them right away.
A preview of the document helps authors tune the paper for the paper publishing format used by the conference. For example, limiting the code-blocks line length to make sure they do not overflow the page for the indent values used when publishing the proceedings.
Collaboration is made easy by the Git version system features and the commenting and change-tracking features of the editor.
Reviewers can add comments directly linked to the section that they refer to. Also, in case of multi-round reviews, it is easy to see a difference between the two versions of the paper and to check how their comments were addressed.
Having the papers in a structured format and respecting the imposed constraints, it is easy to publish them in multiple formats. Also, since authors have the opportunity to preview their paper published with the official formatting, the quality of the output should be better.