"Maintaining" strictly means enchantments that require an upkeep cost of -1 energy regeneration. No other enchantments count.
This skill effectively reduces the energy degeneration caused by maintained Enchantments to 1/4, assuming it is constantly used as soon as it recharges and does not get interrupted.
The Mesmer skill Mantra of Inscriptions is often used to increase the number of enchantments that can be maintained. At high enough ranks in Divine Favor and Inspiration Magic, this will result in a net energy gain, not just a reduction of loss.