When publishing existing layers of data from my ArcGIS server to ArcOnline, it would save a bunch of time to have the metadata (Item Description) already existing in ArcCatalog to transfer over when the data is published to ArcOnline. It is pretty time consuming to have to copy and paste the summary, description, credits, tags, and use limitations from Catalog to each Item Details in ArcOnline. After talking with Esri support, there currently isn't a shortcut.
I've also provided a screen capture of the Item Description one would see when you click on a feature class in ArcCatalog. The categories are the same as fields users fill in for uploaded content.