Mastery Challenges

First of all, as a feature request, you need to add a search function to be able to search specific forum topics (like feature requests).  I would gladly have run a search to see if my question had already been addressed, but I am not about to waste hours and hours reading all the hundreds of pages of forum posts to see if it has ever been asked before I post it..

As for my question, can someone (official) PLEASE explain to me why it is necessary to place the waiting period between mastery challenges?  Why can't students just keep repeating the mastery challenges as a way of reviewing and mastering material???

I would also like for someone to give me an explanation of how the quizzes, unit tests, and course challenges are set up and how they affect mastery. 

For example: The practice is pretty straightforward: you answer 4 questions; if you answer 3 right and you achieve "familiar", get all four right then you achieve "proficiency", but to level up to 100% mastery on any given skill you must take the unit test, course challenge, or mastery challenge.  BY FAR my preferred method of course mastery is to level up ALL skills to proficient using the quizzes and practice exercises, and then use the mastery challenges to level eventually achieve 100% mastery.  I just wish I didn't have to wait so long between master challenges! 

The unit tests and course challenges suck (especially for the higher level courses like calculus) because they take SOOOOO LOOOONG to complete and you literally have to do everything perfect to level up skills.  I like the dynamic of the mastery challenges where if you get 2 questions for each skill and if you get them both right you level up, if you get only 1 of 2 right then you stay the same level, and if you miss both then your level drops.  WHY CAN'T THAT BE the formula for unit tests and/or course mastery challenges as well?!