What Taxonomy Terms to Aggregate

I'm working on an Aggregation site. I am using FeedAPI to pulling the feeds. I have a vocabulary for "tags" and "category." I assign each feed at least on "category" when the feed is created. I control the create of the Feeds and the "category". The "category" vocabulary also drives a menu on top of my page. I am using Feed Element Mapper to add tags from the Feeds to the "tags" vocabulary so I have no control over what gets put in it.

I am also using Messaging/Notifications to allow the users to subscribe to feeds and/or "category" vocabulary.

I am thinking of allowing users to subscribe to the "tags" vocabulary. I am not sure about this because I do not have control over the "tags." Anyone have any benefits or possible drawbacks to allowing the users to subscribe to "tags?"

My main reason for allowing it is due to a feed can have a wide spectrum of categories. This would allow the user more control over what they see. For example, one of the feeds covers cooking and technology. So one post is a recipe, then the next is about web design. The person subscribing to the "recipe" cateogry is now going to get web design items because the feed is catorigized as both recipe and web design. Using tags would attach the subscription to the actual post instead of the feed.

I also worry about giving the user to much control. My audience isn't necessary a technical bunch of people and I attempt to follow the KISS (Keep It Simple, Stupid) methodology.

Cheers and thanks for the suggestions!