If your soaking and not pumping them up all your doing is coating the lifter with oil, a job you could do just as your installing them.
If your soaking and pumping them up read on:
A lifter filled with oil will not be able to be per-adjusted correctly and when installed your going to have valves that are open when they should be closed due to the lifter being full of oil when it should be bleed down.
What's going to happen is when you attempt to start the engine the compression will be all fWONked up so cylinders will not fire as they should so your attempting to start the engine with bad very little compression.
The lifter get it oil from the oil gallery in the that goes through the lifter bores. It enters through the pintal hole in the lifter when the lifter is aligned in the bore, The alignment is the tapered or skinny part of your lifter on the side, when this is lined up in the lifter bore it gets oil and bleeds it off through the push rod and then lubes the rocker arm and valve tip/train. With the lifter full of oil it's going to have the outer pintal hole lined up with the inner pintal hole that allows the lifter to fill with oil to not compress and the lifter will hydraulically lock open. They will bleed down but not very fast.
It's better in my opinion and some lifter manufactures like Johnson
The cam lobes get there main lubrication from the oil splash from the crank and rods and, this is why you keep RMP's up when breaking in your cam. So the more you rotate the engine attempting to start it and not getting "splash" the more wear your putting on your cam lobes and the better chance you have at cam failure.
Comp Cams tells you not to pump them up and that soaking ensures they are lubricated on the outside surface.
I voted no...Don't soak them.
http://www.compcams.com/Instructions/Files/COMP4-115.pdf