Its more of a cultural thing at the moment. You are more at one with the bike on a fixie and people can do tricks with that control. However, I rarely see them on serious MT. trails or long distance road rides. Shiftable gears really come into play in these disciplines. Fixed gears are great for local commuting through traffic and aren’t as fragile to curbs and such as traditional road bikes. RIDE EVERYTHING, and then determine what best suits your riding style. My last ride was a fun 28 miler and I was very happy to not have a single fixed gear when riding in traffic 25-30 mph zones. But, I commute to the city, not through it as much. On a Mt. trail… use what feels best but I pity the fixies on uphills.