Quoted from Rdoyle1978:I believe these are looped to get additional voltage through the connection. Not 100% sure though
Voltage would not be affected
Quoted from dr_nybble:My guess is to split the current through two header pins but would love to know for sure
This would be the result and could reduce heat on the connector
Quoted from Mitch:Could you eliminate the loop do a single wire to each and hard solder a jumper between the pins on the back?
you could but then all of the current is on one pin. in many cases those pins are already common on the back of the board.
If the wire gauge is small enough you might get two wires in one crimp connector if redoing with Trifurcon connectors and sometimes not. I use two sizes of crimp connectors for the .156 housings, I have also soldered the wires in the connector pin. Otherwise the forked method with shrink tube is a tidy solution. The pin wiki page referenced by Rdoyle is an excellent resource.
