A couple "definites" for why you would choose a bottom feeder over another mod:
1) You vape high VG or 100% VG. In this case you want to vape directly off an atty, and not everybody can sit around manually dripping.
High VG and 100% VG will ultimately clog cartos and/or clearos faster than if you were using more viscous eliquids. That is just a given.
2) You are spoiled from the flavorful vape that comes with vaping directly off an atty....homemade coils or otherwise.
I started out as a dripper, so I've never been able to use another device. A bottom feeder just allows you to drip without having to actually sit there and drip into the top of a coil/atty.
3) putting juice into a bottle, and squeezing it, is way easier for me than priming a carto, trying to shove a carto into a carto tank and then filling the tank, and dealing with replacing coils and such inside a clearo or wicked tank like vivi nova, etc. With a bottom feeder, you buy a good atty, it will last months and months, or a rebuildable and always have a nice clean fresh vape. Your juice is onboard in the bottle.........easy peasy.