Why does one need to soak the new oil filter before installing it? What happens if it is not soaked?
If you forget to pre-oil the filter cartridge on a UCE, it isn't a major problem.
The UCE's oil pump, pumps over 4.5 liters of oil per minute at 2750 rpm so at a 1200 rpm idle speed it will fill the filter cavity fairly quickly.
Fast enough so no damage will happen to the parts downstream before they get their oil.
That said, pre-oil your filter just before you install it. Any little bit that can be done to help the oil get to where it's needed is a good thing to do.
As others mentioned, this pre-oiling of the filter on the old iron barrel is a lot more important.
The Iron Barrel engine uses a tiny piston going up and down in a short cylinder to pump its oil so it really doesn't pump much oil per minute.
This little pump is also why the Iron Barrels don't have much oil pressure feeding the crankshaft bearings but that's another story.