hi,
does someone know what are the benefits of equiping a dagger over a shield as melee?
do you hit with both weapons at once?
do you only take turns on hits?
does it increase attack Speed?
does the base damage of the offhand go to the mainhand?
pls someone enlighten me 
i believe all stats aside from your daggers attack cross over too your main weapon. you have to use the weapon separately, and daggers have pierce damage. some skills and attributes require your too use a dagger too.
the benefits of a shield are similar. you can block separately (and get a 5.5*level bonus it seems) and some skills require the shield.