I have built wings with and without a wing jig. Although jig building wings and fuses makes them very straight it is also a bit of a pain. My wing jig uses 2 rods that are suspended by multiple plastic retainers that can be slid along the wing jig. Each wing rib must have holes to pass the 2 rods through, the holes must be exactly placed or the wing will go together wrong.

If I am building from scratch I will use the jig because I have already planned for the holes in the wing ribs. But if its a kit then I usually dont bother.