To start I am on the opposing camp, that of metal miniatures, so my opinion might not be liked much.

I firmly believe the “plastic mania” is something GW carefully cultivated over the years to make the production of plastics not only acceptable from the community, but also demanded, separating them from their opposition who, in their minds at least, could not follow them.

So what is the advantage of plastic, for starters its cheap, moulds are on the expensive side, but will virtually last forever in contrast of the RTV moulds for metal miniatures that need replacement every so often, it also allows a level of automation that RTV moulds cannot give because they need human assistance (and extra manpower) they also make inventory easy because all parts of a model (or models) in on one sprue so you must track sprue and not parts and of course any excess is recyclable, all the above are the industrial advantages that have some merit to the modeller is the cost saved from them is passed to him.

Another Advantage is the “plastic glue” since it isn’t a glue but a plastic solvent, two parts melted into a bond will always glue better than two parts held together by a thin strip of adhesive.

The disadvantages in my opinion are many, for starters you loose any organic forms and get models with many undercuts and many unnecessary parts to overcome the undercuts problem, you loose in sculpture dynamic partly because the press mould needs the model to be flat since it cannot do undercuts but mainly to maximise the ease of conversions, that is the main defence I get for plastic models, in my opinion you do not get ease of conversions with plastic models, if you need to cut reposition and greenstuff the model resculpting at least part of detail, then its not an easy conversion, its the same with converting a metal model maybe with a bit easier cutting, likewise all the extras like holsters, knifes, pouches and so on, since they have not sculpted on the miniature, but designed to fit on any miniature assembled from the parts of the sprue, more often than not look like they were just glued on the model than been part of it, on top of al the above you get the usual loss of detail plastic models get.

Metals are not the god send thing either, they cost more, the moulds tend to deteriorate so the last batch of the mould may have serious issues with quality if the company insists on using the mould till the end and not retiring it earlier, are more difficult to cut and do not come with many extras if at all, since many small parts make the inventory storage a hell incarnate, but hold detail better than plastics, can hold organic form and in extension dynamic poses and need fewer parts per model because of this.

For me the things lost in a plastic model are more than the things gained for being plastic, so I prefer metal models over plastic ones.