There is a continuum from scattering millions of tiny eggs to the mercy of their surroundings to the production of only dozens of offspring, each of which is provided with food and protection until ready to fend for itself.
All strategies require expenditure of energy to ensure a next generation.
The energy may be in the form of multiple gametes or of extended care of a few. Although closely related species usually use similar spawning strategies, there is no general evolutionary trend from primitive to advanced groups. Eggs are provided with only enough materials to get them to a self-feeding larval stage. Larger eggs would be more conspicuous and thus have a reduced survival. Advantage - dispersal by planktonic drift of larvae.