Well metal, in the case of large castings that are not hollow, can suffer from 'cream egg syndrome', which can be really dangerous for the poor sods who have to pull it out of the mould. Basically, it can be cool on the outside, but liquid on the inside and very eay to crush allowing hot metal to go everywhere.
Resin is a cool casting process with little to no shrinkage rate as well. It is the best way to recreate a sculptors original model. It also doesn't use the spin casting technique used in common Metal Miniature casting, which can put up to 10,000 tonnes of pressure on the sculptors master. This can damage and warp the Master piece and can also be quite limiting (the guys I sculpt for once recieved a miniature that was sculpted over a corrugated cardboard dolly which allowed the mould to crush hours of work!), resin will not do the same thing.
This can mean;
a) Better Detail, as sculptors are allowed to go to town.
b) Better poses (possibly) for the same reason as above.
c) Better 'fixing', it's rare that you will get shrinkage or 'pitting' which occurs in metal casting, usually when the metal cools down too quickly
d) Happier workforce, if not from the resin fumes, at least from the lack of dangerous hot metal nastiness (ever tried pouring hot metal into a cold mould? Not nice, gets hot metal EVERYWHERE, not recommended).
It's great for conversions too, much easier to cut, saw, snap etc... Making your own damaged ship counters etc should be very easy.
Judge Dredd Fatties in resin would be brilliant, I've been trying to convince my boss that some similar sized minis really need to go to resin...