As compared to lead or pewter miniatures, all of which can be used in tabletop games and RPG's. Plastics have the advantage of being cheap, so you can have a whole regiment of skeleton knights for what you might pay for one really cool demon in pewter or lead. Plastics are also easily vivisected and recombined with a hobby knife and some airplane glue, so if your taste runs to the bizarre you you can home-brew some really chaotic creatures. This is great in games like Warhammer, where some of the creatures get random Chaos mutations.

miniatures | abortive projects | Chaos mutant