One good reason is to shed the weight and drag of nosegear. Another is I like to mount my engines (two-strokes anyway) with the cylinder about 7-8 o'clock, so as to put the muffler right at BDC for better static & aerodynamic balancing. Third is, with noise becoming more an issue, pitts style mufflers are not as effective at sound reduction as stock mufflers, or the PSP tuned mufflers which I like. I say pitts because the last way I would mount a two-stroke is upright, because of fuel tank placement issues. So if I had a tri-gear model and wanted to keep it that way, a pitts is the only way I can get the cylinder inverted and keep the muffler off the side (for aerodynamic balancing) and not have the muffler occupy the same space as the nosegear. Finally, as you get into the more advanced models, they are mostly taildraggers and you have to learn how to handle them sooner or later if you want to progress beyond the simple stuff.