Since Flash files are typically placed on the Web, the smaller you can make the resulting file, the less of a headache it will be for viewers to download and enjoy them. There are a number of steps you can take to optimize your project so that it will be a smaller final file.
Particle layers can be exported to the Flash SWF format, but each separate particle takes up memory, so complex particle layers with hundreds or thousands of particles can very quickly bring the SWF file to its knees. If you plan on exporting the project to the SWF format, try to keep the particle layers to a minimum.
To limit the number of particles that are exported, simply enable the Reduced Particles option in the Export ...