So yes. We render everything in triangles. It's faster. Drawing Quads is terrible. Sometimes you can't help it, and thats fine. But you should never render everything as single or double triangles, and thats exactly what GameMaker does. So yes Dark Matter; Drawing 2 triangles at a time is always bad, but sometimes you can't help it.
In GameMaker this is true, but for big 3D engines? No sir.
You see, quads aren't slow. It depends entirely on how it is programmed. Infact almost all effects, including particles, are based on quads. Modern games have thousands of particles going about, all quads!
The trick is this. Groups of particles are merged into a very small amount of primitives, as that will make them render very fast, just like any other model. Then they use realtime vertex manipulation
on models to make the particles fly individually. If you can provide GM with functions to manipulate vertex data on the fly, quads won't be any problem whatsoever. Although then the bottleneck would be GML... but well, better than nothing. And there are more uses for it, like realtime deformation.