Time Controls: Time in-game can be rationed via time gates. A time gate prevents one player from getting ahead of another player just because they have more time to play. Turn-based games like chess and checkers do this automatically. As soon as you remove all time gates players will be motivated to win your game by not sleeping (or eating, or working, etc.). This has substantial negative effects on revenue generation (a full discussion is beyond the scope of this paper).
Note that a time gate need not strictly use a time metric. It can also ration a player's actions. Zynga does this in all of its products via the energy resource, as an example. This is a preferable approach to using time itself as the control, as a player will get aggravated if real life draws their attention or they fall asleep at the keyboard and return to find their time has expired. The greatest weakness of the Zynga time gate is that it can be bypassed completely with money, thus breaking it.
A game without a time control is a bit like an "all you can eat" restaurant. This works for some restaurants because they can just keep putting out cheap content forever. As a game developer, very little in the way of attractive content is "cheap." Once a player has had their fill of your content, they will move on as there is no way you can create content as fast as your gamers can consume it.
Uncontrolled time also acts as a Supremacy Good, with the added disadvantage that you are not being paid for it. This will make your game much less attractive to those players with huge money budgets and small time budgets (your ideal customer).
When you sell game advantage via any of the above methods, you break the game intentionally. I would go so far as to say your product is no longer a game, but just an entertainment product at that point -- as described in the aforementioned Game Monetization Defined paper. Further, when you make the game highly competitive between players you create what is in reality an ante game, as described in my How 'Pay to Win' Works paper.
An ante game is one where you can win just by raising the ante to the point where your competitors cannot match you. Skill and effort become irrelevant. Most Facebook ante games (currently all mid-core and Asian browser games) have no cap at all.
Some games, like EA's browser-based iteration of its Command & Conquer franchise, have such high caps that the game still becomes an ante game. This has negative effects on revenue generation, as further detailed in my Supremacy Goods microeconomic model.
While your "hardcore" gamers (I define these as playing more than two hours per day on average, and typically eight or more hours on at least one day per week) may be your most vocal, they are not necessarily your biggest spenders. The person with a job, high income, and very little free time will spend a premium for quality entertainment on those times when she does have time to play.
Creating a game that provides a quality experience for these high-budget, relatively casual players without resorting to Supremacy Goods should be the ultimate goal of a well crafted monetization design. Obviously exceptions will occur in the case of niche products, but those niches can get crowded very quickly, leading to rapid loss of positive net income.
Just as there are almost infinite ways to craft said design, there are also just as many ways to really foul up your design. The key is to know your consumer, and how any change you make to your design will affect the relationship between you, them, and your product.