I have heard that it is beneficial to take vitamin C when you are experiencing cold symptoms.
I don't know there is any actual evidence that it works for colds, but it does prevent scurvy.
What exactly is scurvy?
Scurvy causes weakness, feeling tired and sore arms and legs.  It can cause death.
Has it been proven that vitamin C actually prevents scurvy?
Oh, yes!  Sailors routinely died of scurvy before limes were standard to be brought onboard ships.  Now it occurs mostly in those with alcoholism
I have never heard of limes being a staple for sailors in order to prevent scurvy!
Yep.  They were something that could last for a while onboard.  Lemons as well.  I believe the British Navy started the program.  It takes at least a month of too little or no vitamin C before scurvy sets in