Lonewolf50 - Well the most obvious one is time on station. Since they are still doing visual SAR, aircrafts from a LHD (SH-60s, CH53s and MH22s etc can fly multiple sorties on the search area instead of just having a small handful of aircrafts taking turns one or two at a time flying out of Pierce AFB over a thousand miles away.
A lot of the helos are also outfitted with sensors sensitive enough to pick up a periscope potruding from the surface soi I'd imagine similar sensor can be tweak if necessary ti pick up metal debris etc.
A LHD can also operate independantly w/o the need for escorts etc to lessen the operational costs of having an entire CSG there and be almost as effective.
anyway just my 2c.