So bigspenda are you saying you calculate exact odds\percentage in your head with more than one card to come? Someone pushes all in on the flop and you have a gutshot + flushdraw which gives you 12 outs and you solve this equation (1-(35/47*34/46)) in your head? Im guessing you dont multitable then?
The 4 and 2 rule is a pretty good approximation of your odds (especially when you correct for outs more than 8) and is very useful when you have to calculate odds on the spot.