With a pressure-based system, you trade off some accuracy for simplicity. Air pressure isn't always equal to height, so in some situations you'll end up needing to manually adjust your vehicle to level it back out- like if you have the trunk loaded down, a REALLY heavy passenger, etc. This is only common in extreme situations- for most day-to-day driving a pressure-based system will keep you rolling just fine.
If you decide later down the road you'd like to upgrade to height sensors, you can just pick up the Height Sensor Upgrade package, change a few settings, and you're good to go!