I believe the light fighter is used as fodder only in fleets. The ogame combat targeting system is based on random targeting, which means every ship is equally likely to get hit no matter how big or expensive it is, or small and cheap. for example, if you have 2 cruisers for the price of 14 fighters you will have your 2 cruisers shot and destroyed by 2 hit from a big defensive gun. If you had a mixed fleet of fodder and attack force (say 7 light fighters and 1 cruiser) then those same 2 hits from a big gun each has a 1 in 8 chance of hitting the cruiser...which means you're more likely to lose a fighter instead. This saves you resources, and allows your cruiser to still be in the fight. Make sense? Use fodder in your fleets, and in your planet defences to protect your big expensive ships/guns.