Items that might seem drains on the budget may in fact be boons.
late 12c., bone "petition," from Old Norse bon "a petition, prayer," from Proto-Germanic *boniz (cf. Old English ben "prayer, petition," bannan "to summon;" see ban).
in boon companion (1560s), only real survival of Middle English boon "good" (early 14c.), from Old French bon (see bon).