Originally Posted by JohnDThompson

"Heavy duty" in the context of a torch refers to the material you'll be working with, e.g. thick steel plate, etc., not the overall sturdiness of the torch. With steel bicycle frames, you'll be working on thin tubing and sometimes in tight spaces a "heavy duty" torch would have a hard time reaching. Smaller torch bodies can hold smaller tips, which come in handy for delicate work with braze-ons and such. I used a Smith AW1A at Trek, and it was just the right size. It can hold a big enough tip to heat heavy pieces like bottom bracket shells and fork crowns, and small enough tips for more delicate work.