Gaming theory: Set interval reward mechanics

Set interval is a player reward mechanic that regularly rewards a player upon reaching a specified interval (such as completion of a task). The reward itself may be randomized but the player has the assurance that when the interval is reached during gameplay, they will be rewarded.

Cons
Set interval systems require significant planning and programming/implementation to balance gameplay and progression
As complexity of game increases, the amount of work going into planning said systems increases, sometimes exponentially  (More below)
May be simpler to let players choose rewards rather than automating rewards

Pros
Often an ideal choice for progression systems (if progression systems are universally equal for all player options)
Consistency of rewards to efforts reinforces player expectations
Easier to plan escalating challenges with due to higher consistency of gameplay milestones

Commentary
Example of increase: game starts out with two player options - classes each with unique tools to aid their efforts; as a third option (class) is added a set interval reward system would ideally need to create a reward set specific to that option to adequately reward the player rather than giving them a chance at rewards useful to them which are tacked onto the rewards set of the other options.

Definitely less exciting than random interval reward systems, but set interval's strength is in long term planning and use. Set interval establishes reliable rates and is a staple of complex and/or lengthy duration games.