What is the ideal period for content that is meant to be repeated?
For example, WoW has quests which you can do once per day. Raid dungeons, on the other hand, can be done once per week. Is one time interval better than the other?
Part of the issue is that rewards tend to map towards how often the content can be repeated. The shorter the period, the smaller the reward is. Dailies in WoW tend to reward about 10 gold. Rewards are balanced assuming that people will do the content as often as possible. This is because there are people who will do the content as much as humanly possible.
Instead of having a daily quest which rewards 10g, would it be better to have a weekly quest that rewarded 70g?
I think it comes back to how people play. Are people (who are working on repeatable content) more likely to log in every day for small amounts of time, or do they log in less often but for longer play sessions? My personal thought is that the second alternative is a better fit for most lifestyles. Balancing around a period of a week might be better than balancing around a day. You could even make the quests a bit more involved.
However, there are two repeatable quests which I think are good as dailies: The daily Heroic Dungeon and the daily Battleground. These quests work best when there is a large pool of potential players, and having a fresh quest each day means that it will be easier to find a group.
To sum up, repeatable solo content and fixed group content are better off on a weekly basis, as this allows players to better make use of the time they have available, without being pushed to play every day. However, repeatable ad hoc group content is best on a daily basis, to make forming groups as easy as possible.