ya garvo slopped a few hogs in my day,  could never see the advantage, also had pigs that had anniversaries before they left the farm.   don't ever remember slopping oats, and believe you me we had a lot of oats.   my grandpa was watching me grind feed one day many years ago, he started asking questions about rate of gain, feed conversation, days to market, etc..  he used to have a soaker/ slop tank.  he confided in me that he thought soaking grain was a waste of time for pigs, but it was what everybody did.