...I can't really see any build which makes marauders preferable to warriors.
Whether Warriors are better is a different (and possibly clearer) question. I was interested in whether if you are taking Marauders (maybe as part of a fluffy army) it is better to take light armour.
Gathering together the discussion here and elsewhere it seems that against attacks <= Str 3 LA saves more models than you could buy with the points. Against attacks > Str3 LA is worthless. The X factor in just Mathhammering it is the lack of a clear answer on what proprtion of attacks will be Str 4+.
So my unscientific conclusion is that if you are using Marauders for a defensive role it might be worthwhile once you have bought the unit up to a useful rank bonus.