The main use is not, most of the time, to decide if we will go or not, for most airlines that is decide by the dispatcher, or ops / OCC (depending where in the world you are and what system the airline uses). The general rule is that for +/- one hour of your expected arrival time at destination or alternate the weather must be forecast to be above specified limits depending on the type of approach to be used, and that information can only come from the TAF. Having looked at that we can then look at what fuel the flight planners have chosen and decide if we want more if, for example, the wind is forecast to change giving a runway change and maybe longer routing needing more fuel, or if visibility may drop with possible delays if LVPs are going to be in force. Quite often, depending on type of aircraft and route we may have a trade off between load we can carry (passengers/bags/freight) and fuel, just like in a light aircraft. As a rule company ops will want us to carry as little fuel as possible and we will want to carry as much as we can possibly justify (unless we’re managers or training captains !! ), so the TAFs are very necessary.