Question about on/pri/res positions

[Ololorat]

Hi guyz
I have a question:
In cold weather I couldn't start my bike and just tried PRI position and engine started to work. From description in manual it doesn't look that PRI position could help (I use my bike often and didn't drive just for couple of days so there was no lack of fuel in carburetor).
Does it mean that in ON position something can be wrong?
Also in manual it is said that "Upon starting the engine, be sure to return the fuel valve to the ON position". So is it going to be a problem if I drive when valve position is PRI (I read manual after doing that)