the liners are now preformed using a new (and very clever) process in the factory, that said they are not formed to YOUR feet, i guess it all depends on how it feels when you have the boot on, heat forming will help if you have specific pressure points around the foot, but isn't a requirement..... if you are in a really short shell check heat forming with toe caps will give you more toe room, if the boot is the slightest bit on the generous side i wouldn't heat it
so every case is individual