There are a few use cases:
1) The high speed player who never hits 3 wood off the deck - replacing 3 wood. This player also typically plays a fade with their driver and wants a club they can draw as their second tee club (or vice versa).
2) The player who can't hit driver, but can hit a fairway wood pretty well. A Mini-driver with more loft and a shorter shaft allows them to make more of a fairway wood swing. - replacing Driver. This is a band-aid, but not everyone has the time or willingness to work on their golf swing and that is ok. If it gets the job done, then that's all that matters.
3) The low swing speed player who needs more loft to elevate and spin the ball. A mini-driver or a higher lofted driver could work here.
4) The half-set minimalist who wants to get down to as few clubs as possible and enjoy a different type of game.
I'd say it's more about your swing speed and impact dynamics than your handicap. And, it's pretty unlikely that it serves effectively as both your tee club and your longest fairway club unless you are a pretty skilled player in category #4.
