Master Calendar , has its own need based on the data and the requirements in hand, few examples are:
1. You need to create the missing date for instance , if you are dealing with Sales data and a product has no sales on a particular date then that date will not have an entry in the table, so now in case you want to display on which dates there were no sales of this product , you cannot do so without generating the missing dates using a Master Calendar
2. Supposedly you want dates starting from the first order that got placed til the last order that got delivered both of which are from different tables, Master Calendar comes handy
3. In case you need to create a Fiscal Calendar
So the use cases of a Master Calendar depends on your need
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Here is the base Design Blog link which I think I have provided previously, please be sure to search there as there are over 700 posts in that area and most are how-to related, so should be very informative for you.
To help users find verified answers, please do not forget to use the "Accept as Solution" button on any post(s) that helped you resolve your problem or question. I now work a compressed schedule, Tuesday, Wednesday and Thursday, so those will be the days I will reply to any follow-up posts.