It's the same reason we used metal spikes when playing baseball and the 3/4 inch screw-on plastic spikes while playing football - for traction. I don't think there are any golf clubs that allow metal spiked golf shoes any longer. The reason is that golfers would wear them into the club house and the Proshop and the spike would cause damage to the wood floors, tiles, carpets, etc.

You don’t have to use them. They’re supposed to help with stability, traction and grip, though. They also help a lot if the coarse is wet or hilly, but it’s up to you. It’s kind of tiring when you’re going up and down hills on a coarse, especially if you’ve got no traction and it’s a “cart path only” type of day. But, many regular sneakers these days have a lot of traction. I live in Florida and we get a lot of rain some months and I don’t know if regular shoes would be adequate. Lastly, you probably want a pair of shoes dedicated to golf because if it is wet or muddy, you don’t want to bring that in your car when you’re done. Most players change them out and it gives them a chance to dry, not stink and last longer.