The vfork() function can be a lot less resource intensive than the plain fork(), because it shares the parent's address space.
The vfork() function creates a child, but then suspends the parent thread until the child calls exec() or exits (via exit() and friends). Additionally, vfork() will work on physical memory model systems, whereas fork() can't—fork() needs to create the same address space, which just isn't possible in a physical memory model.