Specifically its WebDAV file shares. Basically you have a tickbox for each of your shares for each protocol you want to use. One of them is labelled "Share with iOS devices" or similar, but it means WebDAV.
Supposedly you can then connect using Command-K from another Mac and
http://X.X.X.X/webdav/user though I haven't gotten this to work at all. I have persuaded it to prompt for login credentials using
http://X.X.X.X/ or sometimes
http://X.X.X.X/user and for certificates using SSL but regardless it eventually gives you a totally useless "there was an error" or "IP is wrong" error message and Console reports that WebDAV is not supported for that share.
I've checked the Apache config files, the various WebDAV config files and the virtual host settings, everything I can find looks like its properly set but nothing will successfully connect to it via WebDAV. The only thing both servers have in common is they were upgraded from Snow Leopard Server. I supposed I ought to try with a clean one just in case.