Flickerstreak pretty much nailed it, the only thing i would add is that you should know that there is a render options tab in bryce that you can click that will let you adjust the rendering quality settings for several things or turn them off. These include antialiasing, spatial optimization, gamma correction and 48 bit dithering, turning this stuff off considerably speeds things up for test renders. You can turn it back on for your final and go to a movie or whatever... I also use Roobols strategy of rendering large without the extras and then downsampling in photoshop and it seems to work pretty well.