Noct allows you to play more aggressively if you're into dealing damage as a healer - you religious sect of non-dpsers stay in the other topic, please.
Aspected benefic in noct is a bit over 600 potency combined, giving you access to a rather potent instant healing at any time. It is not spammable, however - you can, but not recommended to fill up hp bars. It's also perfect for snipe healing players who get low on health for whatever reason and may die to the next AoE. The Vault bosses are probably the best place to try out noct sect.
If you're not into that, stick to diurnal for most of it. It doesn't really matter much till you reach 8-man content. Although you should take the opportunity to practice both sects before you get tossed into the lion's jaws