As tek said, the value of providing sugar/carbs appears to be to the microbes in the soil. For example, if your medium has myco it gets its sugar from a symbiotic relationship with the plant where the plant translocates carbs from leaves/stems to the fungal partner through its roots. The plant benefits from myco's higher absorptive capacity for water and mineral nutrients.[1] Ergo, supplementing carbs leads to a greater benefit than the plant could "cultivate" by itself.
Honey is an interesting concept. In naturopathy it's considered an antibiotic. In growing we often hear the word "bacteria" qualified as "beneficial" (aerobic vs. anaerobic). I suspect people into natural remedies would prefer honey over molasses.
I think the usefulness of sugar depends on whether you grew with a mind toward promoting a soil biology. If you feed synthetic nutrients in 100% soiless, it's probably pointless. The more soil in the medium and/or organic nutrients/material supplied during the grow, the more biology and possible benefit to sugar.
@churchhaze mentioned last night sugar creates a hypertonic condition in the soil, drawing water water from the plant.[2] So, don't get the idea more is better.
[1]
http://en.wikipedia.org/wiki/Mycorrhiza#Sugar-water.2Fmineral_exchange
[2]
http://rollitup.org/t/what-supliments-to-use-with-general-hydroponics-floranova-bloom-thanks.844877/page-3#post-10903893