This may be most relevant when a new user starts configuring Simplifi to meet their needs. Currently in the Transaction view, when going through and assigning categories, if a new category is needed I need to switch over to the Manage menu and enter the Category and Tags maintenance screen from there. And then when I'm done I switch back over to Transactions and find where I left off.
I suggest creating some sort of quick category maintenance function right in the Transactions screen. Perhaps a small floating popup. Or simply the ability to type a category and if it is not recognized, a prompt to add it and (optionally) its parent. I think MINT has this capability.