caching (e.g. via cachinghoster and/or caching-store) can be used to reduce expensive computations
indexing (e.g. with the tiddlywebplugins.whoosher plugin) can help with searches across all tiddlers
a customized store implementation might be used for efficient data mapping

having lots of bags is far better than having bags with lots of tiddlers in them
when filtering a bag, TiddlyWeb looks at every single tiddler in the bag

<cdent> if you know that you are always going to be doing a particular filter, that might be sign that you actually want to have a bag that indicates that state, rather than a field