So, bidding should be leisurely when bidders have little to learn from each other (say, when they're bidding on a new computer that's been widely reviewed) and intense when some bidders are far more expert than others (say, when they're bidding on a heart defibrillator for home use).
When bidders don't have much to teach one another, there's no need for bidding to be done intensely.
When bidders aren't necessarily more expert than each other, bidding should always be intense.