A git wiki page is a wiki page whose type has been set to Git Repository. Once a page has this type, the folder that holds the page's resources also serves as a bare git repository that people can clone from and push to over the web using an ordinary git client. The settings in this fieldset control how new git wiki pages start out and how large the data pushed into them is allowed to be.
Turning a wiki page into a git repository is not offered to everyone. It is controlled by a modifier on the Feed and Wiki activity in Manage Roles. A role that carries the no_git_repository modifier cannot create git wiki pages. Out of the box the Admin role can create them and the ordinary User role cannot. To let another role create git wiki pages, remove the no_git_repository modifier from its Feed and Wiki activity; to stop a role, add the modifier.
The branch name a brand new git wiki page starts its empty repository on, for example master or main. This only affects repositories created after the setting is changed; repositories that already exist keep the branch they were made with.
The three size caps limit how much data a client may push. Each is chosen from a dropdown offering sizes suited to project scales from Micro up to Extra Large, plus Unlimited which turns that cap off. Sizes are written in metric units, so 10M is ten million bytes and 1G is one billion bytes.
A push that breaks any cap that is switched on is refused and the client is told the payload is too large. Leave a cap on Unlimited to impose no limit of that kind.
The dropdown choices follow rough project scales:
Pick the scale that fits how the repositories on this server are expected to be used. Because this server does not use large file storage, keeping the caps modest helps clones and pushes stay fast.