You won't necessarily hit more often, but rather "miss" less. That is to say, if they don't parry/dodge/shieldblock/etc. your strike, you will be less likely swing a miss if you have a higher % in that weapon. Also, for damage, if you know a weapon 75% then you do 75% damage with that weapon, and so on up to 100%. That doesn't take into accout weapons that are much higher in level, but in the interests of keeping it simple... there it is.