A new podcast is any new content since last sync/refresh and should be marked/hi-lighted appropriately until it is downloaded or dismissed.
The reason I don't have them all set to auto download is because many of my podcasts subscriptions are music related and I'm not always interested in listening to them, also I don't want to open musicbee for it then to proceed in downloading a bunch of podcasts which could be hundreds of MB.
If you are going to include an option for manual download then surely there must be some sort of system for notifying the user of new content because at the moment there's no obvious way of knowing, unless you check dates/descriptions yourself, which is not very good!