Uncoilers are feeders for a duct line or a plasma table.  When purchased for a duct line the contractor can buy up to four decoilers, one for each gauge of metal. 

 

The underfed comes up a ramp and the pinch roll pulls it in.  The downside is it costs more and it takes up eight additional feet of space.

 

The overfed is not so gently referred to as a drag off setup which means the operator has to get up above the coil and pull it down manually which means the operator and a helper have to get positioned to pull it down manually and feed it into the shear (the next step is the shear).

Underfed is going to require more of a footprint (8 feet longer) because it requires more space for the feeding ramp but it is easier on an operator because with overfed they have to pull the metal down.