If you are watering properly, you plant should never be so wet that your roots rot; regardless of freshly repotted or established root systems. That being said; I've always watered trees into their pots, generally I submerged the entire pot for 10 minutes.
What this person doesn't realize is, that pruning ficus when they are wet invites fungus into the trees, and ficus are totally susceptible to fungal rot. If you were to allow your ficus roots to seal over night (the sap is latex) you aren't preventing the roots from rot induced from over watering; you're preventing the chance of fungus entering the roots. I don't worry about this at all though as the chances of the tree drying out too much and dying are greater than coming down with fungal rot.
@KennedyMarx; remember that spaghnum moss is also a natural antiseptic and is chock full of root hormones. Never heard of anyone doing an air layer with bonsai soil though; not saying its not possible or never been done before.