It is now used by historians to convert an Islamic date into a Western calendar when no other information (like the day of the week) is available.
It is used by some Muslims in everyday life, particularly in Ismaili and Shi'a communities, believing that this calendar was developed by Ali.
And this is approximately how long it takes for the moon to make full lunar cycle.
As an attempt to make conversions between the calendars somewhat predictable, Microsoft claims to have created this algorithm based on statistical analysis of historical data from Kuwait.
Tabular Islamic calendars based on an 8-year cycle (with 2, 5 and 8 as leap years) were also used in the Ottoman Empire and in South-East Asia.
In the Dutch East Indies (now Indonesia) into the early 20th century, the 8-year cycle was reset every 120 years by omitting the intercalary day at the end of the last year, thus resulting in a mean month length equal with that used in the 30-year cycles.