I have to agree with vmxa, here. Catapults are definitely not junk. Greek hoplites defending hilltop towns? A stack of ten catapults can save you three or four units a turn and give your horses and swords a fighting chance. Opponent built the Knights Templar and your knights and MI have to root them out? A stack of trebuchets can ensure the crusaders don't survive to counterattack with their superior attack strength. Don't have the tech lead and end up facing infantry with your cavalry? Bring along 20 cannons and get those odds in your favor. Your cavarly won't get to move as fast, but they'll still be around to take on the next infantry-infested town instead of dying in droves and ruining your economy.
With a stack of bombard units around, you can start a war, then end it with more units than you started with. Without them, you'll need a recovery period before you attack again, and wo betide you if the enemy senses your weakness in the meantime.
Edit: I meant to add that keeping your units from dying also goes a very long way in preventing rampant war weariness. Not such a big deal if you love Monarchy, but for folks in Republic, this can mean the difference between having the time to cripple the enemy, or having to make a desperation peace on unfavorable turns (the AI knows when you are having issues with WW, and will adjust peace offers accordingly).