You probably mean Area Target Type, not Area Fire. Area Fire is the halving of non-ordnance FP for various reasons. Area Target Type is a Target-Type option for ordnance. Because both rules involve halving of FP (one of non-ordnance FP, the other of ordnance FP) and the word "Area", it is very common to mix up the two. Don't do it.
Also Area Target Type can be direct fire (which is not an ASLSK term, I believe). In ASL direct fire is all fire (using any Target Type) by ordnance except MTRs. One can choose the Area Target Type over the Infantry Target Type or the Vehicle Target Type.
The Area Target Type is better at longer ranges, especially by weapons that use red TH numbers. It allows acquisition against a concealed unit/empty hex, which in ASLSK is not that useful, but can be used to prepare a hex where you anticipate the enemy will move. The Area Target Type can affect both infantry and tanks in a hex. The Area Target Type can give some guns a (slim but better) chance of affecting a tank when using AP against it would not work or is not available. Area Target Type must be used by MTRs.
JR