We all love parallel-type clamps (K-body, in my case), but they are fragile and can be outmatched in rare situations.  At that time, nothing -- and I mean absolutely nothing -- can match the 72xx series I-beam bar clamps.  I've been using these somewhat infrequently over the last 22 years and, while they are not as all-around useful as the parallels, they can come to the rescue on super-stubborn situations, usually involving existing structures or supertight multi-dado glue-ups or, lets admit it, a complex, super-strong design which has gone wrong and is curing fast!  Whaling away at these situations would be futile and throwing on more parallels takes away your control: Just set up a couple of pulling cauls and clamp each end with a 72xx series clamp.  I've also used them to pull tough 4-1/2" tropical hardwood flooring into place (unruly and cruel ultra-dense woods).  Nothing else offers 1,500 lbs of clamp pressure -- no better than half as much, in fact (750 lbs on a K-body or Jorgensen or Gross Stabil parallel, which risks damaging them and would cause a frightening flex to their bars, taking away their parallel attribute at anything above 200 lbs).  I only need these 72xx clamps less than 1% of the time, but that has been enough to make me very, very glad to own a set, the same way I feel about spare tires.