The reason that you may want to put some Vicks on your feet is to help you feel better.
When you put Vicks on your feet the Vicks on your feet creates a cooling sensation which can help your feet feel better as well as your whole body feel better.
Other than the cooling effect the Vicks on your feet does not do much else.
I use the Vicks on my feet sometimes when I need to relax and have a cold or just need help sleeping and for some reason the cooling effect of the Vicks Vaporub helps me get to sleep.
The Vicks on my feet also helps relax me as well.
You can also apply some Vicks under your nostrils or on your chest which can help relieve congestion and help you breathe easier.