Question concerning split-supply

In the part-schematic down below which I have found I have a split supply but also an op-amp to create this, can someone tell me why you use this op-amp at all?

Thanks

If the plus current and the minus currents drawn from the supply are near equal (meaning little net ground current) than you can get by with just a voltage divider for the virtual common. If there is a significant difference, then you need the op amp to absorb the difference (the ground current).

There are lots of opamps, you need to read the datasheet for the lm1485, usually the first page indicates what a particular opamp is best suited to.