Why is it useful: Because each time I log in to Fast Coding I have to reset the filter to "uncoded" to see transactions I haven't matched yet.
Who would benefit from it: Anyone who is annoyed by current behaviour and taking 2 seconds to set filter. :) Probably more of an issue for lower transaction volumes because we spend less time matching and proportionally more time setting the filter.
How should it work: Just remember the filter state, but add an indication to the filter icon to show that a filter is applied. (This indication should be added anyway.)