I wax and I notice it. When it needs another wax I can feel it, and as people have said the first place you will notice it is on a flat runout, if you were on 30+ degree slopes all day you would rarely need wax as gravity is helping you get down fast.
I can even be riding and think to myself that heel side is getting a bit sticky, look at the base and sure enough the heel side looks white, go wax the board and its problem solved.
To listen to some in this thread what I am experiencing is some kind of delusional mind trick engineered by the wax makers. Im not that dumb, I wax when I can tell it needs it and for me that happens to be around very 5 days or so.