The last statement is not entirely true,Ins co.'s are getting away from straightening, and sectioning frame rails, anything other than a slight tweak gets replaced, engine out blah,blah$$$$ This is why. A folded up rail is just that, it's done it's job as they are designed to collapse. Fishplating and or sleeving the rail you have taken away the ability of absorbing the collision impact.The cabin collapses instead. If it's still slightly crumpled it collapses to fast. You have altered air bag timing. The rebuilder can straighten it , mud it, paint it,cover the damage up, throw some used(no warranty and some states do not allow this) air bags in it and call it a day. The new ins. game with these salvage cars , you bid on salvage, pay, the ins mails title (paperwork takes a few days), and it's marked "parts only" Do your research , I'm seeing this more and more. Cars and bikes. Alot of cars by time you write up sensors ,bags, dash panel, seat belt pre-tensionors, clock springs they're close to total already. And yes it's all about liability, and they look at the repair time and rental car bills. No defending ins. co., but dealing with them all the time it's about cutting the $$ and minimizing losses.
