Purpose of this resistor?
Some resistors are designed so that they will fail open when they overheat.
An advantage of such resistors versus fuses is that when failure is a result
of an output short-circuit, the resistor will limit how much current will
pass in the time it takes to blow.  With 120V mains (170V peak) the peak
current would be about 50 amps, which is rather a lot, but is still much
less than would be able to pass through a "normal" fuse.