How to use FK and IK at the same time

I don't understand the reasoning behind having two separate rigs. If I set FK/IK blend to 0, I can only manipulate the model using FK handles. If I set it to 1, I can only manipulate it using IK handles. If I set it to anything in between I get this weird interpolated behavior where the mesh doesn't line up with either rig.

I want to be able to make adjustments using both IK and FK. How can I accomplish this? The only way I see currently is to use Set FK to IK or vice versa to sync up the rigs, then switch the blend between 1 and 0 - and this has to be done every single time I make any change.