As Keith said, this is also sometimes helpful when getting out stubborn larger skrews
, ie hitting them with same type of hammer with appropriate screwdriver before trying to screw it out, it can help with the door and body ones, to break the dust/paint and makes for a shock to dislodge crap in the thread.
Another good thing is to do this say the night before attacking a section then spray fair amount of crc or something then wait for a day or so. planning ahead is good with a strip down
Also heating up bolts such as in non vital areas or things u know your gunna replace too. But there are various opinions on heating up anything to do with suspension. Personally i cant see how heating up a small area on a leaf spring is gunna affect things too much but an engineer would say something id think