This type of cannons focuses on dealing damage to infantry over small areas and destroying buildings. Usually, howitzers are long-range weaponry. They fire fragmentation ammo only, but their large caliber lets them deal considerable damage even to targets with light armor. The greater the distance to the enemy, the less accurate they are, It is a good idea to keep a truck nearby, to evacuate, or relocate the cannon quickly, closer to the frontline. If you want to lay fire first on specific targets, it is a good idea to deactivate fire at will and pick targets manually. While in defense, artillery can effectively pick targets. Apart from that, you will have little time to assign specific units to specific tasks, so it is best to activate fire at will in such situations.
Self-propelled howitzers have the same characteristics as regular cannons. They are long range, inaccurate and they usually use fragmentation ammo only. Some of the vehicles have decent armoring and they can withstand fire from lightweight tanks. A subtype of such artillery are self-propelled rocket launchers, e.g. Katyusha. Their range is shorter than that of regular howitzers, but their rockets deal higher damage to infantry, especially if the projectile hits in the center of a group. Still, supplying them with rockets takes up more supply points than in the case of regular cannons. Exercise prudence while using them, preferably against large fortifications. It is a good idea to disable fire at will, not to waste ammo.