From the journals of the Entomological Society of America:
Influence of Pollen Diet in Spring on Development of Honey Bee (Hymenoptera: Apidae) Colonies
A 3-year study on pollen and pollen-substitute feeding in spring suggests that there was little difference in effect between the two diets. Feeding the bees a pollen or a pollen-substitute, either one, helped the colonies to build up in the spring — however —
an investment in supplementing the pollen diet of colonies would be returned for situations in which large spring populations are important, but long-term improvement in honey yields may only result when spring foraging is severely reduced by inclement weather.
So, if I’m reading this right… the decision of whether a beekeeper wants to invest money in spring pollen feeding might depend on the likelihood of poor foraging weather, and how stressed the bees are likely to be (larger spring populations might be more important for commercial honey producers and pollination services).
The full report has a cost attached, but you can read the short Abstract online, free of charge.