Neither of these is really a contradiction and I agree with both. Soaking a board is fine - as long as everything is truly a solid-state component. Once you add electrolytic capacitors or other "physical" components, though, you have to use the toothbrush and blot dry with paper towels/equivalent.* Electrolytics are an easy justification - they have a liquid electrolyte inside and are not necessarily completely water-proof. At the same time, physical components such as switches and pots - volume and otherwise - may have grease in them to promote easy physical interaction. This can be destroyed if you soak a PCB with those components on it.
I am careful in my build instructions that a total immersion of a PCB is only possible at a certain stage in the construction - not any further.
* One caveat - I've had many larger boards that may take as many as half-a-dozen rinses or more with a toothbrush and paper towel blot before the flux is significantly removed. That may just be me and the type of soldering I do, though.
Edited by tomb - 3/7/14 at 4:57pm