Quick Questing automatically accepts and turns in quests when you talk to an NPC, so you can fly through quest hubs.
It can also pick your reward by highest sell price, or leave the choice to you (the default). You can limit it to repeatable quests only, and keep an exception list of quests it should never touch. Hold Shift, Ctrl or Alt while talking to an NPC to skip automation and handle the quest yourself.
To protect you from mistakes, it leaves alone turn-ins that cost gold or currency, PvP-flagged quests, quests shared by other players, and non-quest gossip options.
Configure it in Esc > Options > AddOns > Quick Questing, or with /quickquesting or /qquest.

