Membrane fission is necessary for the formation of vesicles in the endolysosomal system and for the division of organelles like peroxisomes, mitochondria, and chloroplasts. In these processes, fission is managed by certain members of the dynamin superfamily of proteins (DSPs). These DSPs are soluble proteins that self-assemble into helical scaffolds that hydrolyze GTP and force the constriction of tubular membrane substrates, leading to their fission. Based on where they function, fission DSPs can be operationally categorized into vesicle dynamins (VDs) or organelle dynamins (ODs). Even though they share conserved domains and display largely similar enzymatic properties, recent results reveal fundamental differences with respect to the size of the tubular membrane substrate that certain VDs and ODs can sever. Substrate sizes encountered during vesicle formation and organelle division are quite different and could have served as physical constraints that forced the evolution of VDs and ODs. Here, we briefly review and rationalize mechanisms for the division of labor among DSPs.The structural basis for substrate size-dependent fission activity among VDs and ODs remains unclear and represents an attractive area for future research.