Some weapons deal damage of multiple types. If a weapon causes two types of damage, the type it deals is not half one type and half another; all damage caused is of both types. Therefore, a creature would have to be immune to both types of damage to ignore any of the damage caused by such a weapon.
In other cases, a weapon can deal either of two types of damage. In a situation where the damage type is significant, the wielder can choose which type of damage to deal with such a weapon.
'and' counts as both types, and the critter needs to have DR against both to resist it otherwise it's getting through in full.
'or' counts as one or the other, guess wrong and the critter gets full DR
Type: Weapons are classified according to the type of damage they deal: B for bludgeoning, P for piercing, or S for slashing. Some monsters may be resistant or immune to attacks from certain types of weapons. Some weapons deal damage of multiple types. If a weapon causes two types of damage, the type it deals is not half one type and half another; all damage caused is of both types. Therefore, a creature would have to be immune to both types of damage to ignore any of the damage caused by such a weapon. In other cases, a weapon can deal either of two types of damage. In a situation where the damage type is significant, the wielder can choose which type of damage to deal with such a weapon.
Basically, a character using a cestus who's up against a creature with DR/? can experiment by trying piercing damage on one attack and bludgeoning on the next and see if one or the other is more effective.
If the same character is using a morningstar he is simultaneously doing both piercing and bludgeoning damage - if the creature is vulnerable to either piercing or bludgeoning damage he'll automatically take full damage.
Since many characters rely on slashing weapons as their primary weapon, morningstars are actually excellent backup weapons. Most of my characters carry a morningstar if they can fit it.
So for all intents and purposes 'and' is better?
yes
Correct.
So for all intents and purposes 'and' is better?
Generally speaking yes, but there are (a few) exceptions - there are times when you do not want to do a certain type of damage. An example of this would be when fighting a creature with the split special quality, like a black pudding. The cestus user would be able to punch it dealing only bludgeoning damage, while the morningstar would cause it to split.