It hits harder at the cost of no Param Bonuses. Raw weapons are good when you're low level and don't have a lot of STR, INT or Faith. But usually the best weapons are the ones that scale (C / B / A / S).
On a side note scaling weapons don't start being good until very late in the game when you have like 30-40 str / dex / int or something like that. Until then Chaos / Lightning weapons are usually stronger.
first off you can only go to raw +5 not +10. and second you can cast temp bonuses to raw and basic weapons, which can be a very powerful bonus. especially the miracle one. you cannot however cast those on devine, chaos, fire, etc.