I feel I should add that conventional cardioid arrays, as mentioned by the OP, have the SPL tradeoff in favor of compactness and reliable pattern. End-fire arrays, as mentioned by everyone else, do not suffer from a loss of forward SPL but do suffer from unreliable pattern control and a much larger physical footprint.
Once you get into large subwoofer arrays, regardless of whether you build in any "extra" directionality or not, you had better have a pretty good handle on how phase operates. It's not just about how the array(s) interact with itself/themselves, but also how they interact with the mains at crossover.
If you're not careful, you can end up with three power alleys, an extremely narrow pattern from your ground-stacked subwoofers, and cancellation that happens at varying audience depths. Solving the traditional left/right stacked subwoofer power alley problem for large PA systems is non-trivial. Modeling is your friend!