If you want to plan what work you will carry out and when, and if you have to make sure this is done in a certain timeline, as well as allow time for holidays and visits to family and friends, then a calendar makes this all possible.
You can see how much can be done in any given month, allow for public holidays when you won't be able to access certain businesses, like banks, and plan the time needed to travel or to prepare for the work you have scheduled within a certain week or longer. You can see at a glance which periods are busiest and where it will be difficult to fit something new in.
Yes, calendars do repeat.
As there are seven days in a week which begin the year and month, you would expect that in every sevens years there would be a repeat in calendar. However, the leap year, which is once in 4 years complicates the calendar.
The calendar can repeat at 5, 6, 11 or 28 years. The only confirmed pattern is that of 28 years. The 28 year cycle works well as long as the 4 year cycle of the leap year continues.
In Gregorian calendar, century years not divisible by 400 is not considered a leap year, for example 1900 and 2100. We are currently in 4 year cycle of leap year from 1904 - 2096 and 28 year cycle is maintained. For example, your 2010 calender can be used in 2038.
It is possible to find repeating year calendars. Calendars repeat in a certain pattern. They repeat in 5, 6, 11 or 28 years interval. The most accurate one is the 28 year pattern. For example, 28 years before 2018 was 1990. January 1 1990 was a Monday, January 1 2018 is also a Monday. The calendars of these two years are the same.
There where 10 months (304 days) in the Roman calendar before Caesar changed it. It was not used for long because it didn't align with the seasons. The 10 months were: Martius (March), Aprilis (April), Maius (May), Junius (June), Quintillis (July), Sextilis (August), September, October, November and December.
There was no January or February on the calendar. March was the first month on the calendar.
Yes, Gregorian calendar is more accurate than Julian calendar.
A normal Julian year is 365.25 days and its an error of 11 minutes when compared to the solar year. It takes the earth 365.2422 days to complete one solar orbit This error in the Julian calendar cause an extra day every 128 years of the Julian calendar.
Gregorian calendar corrects this error by removing 1 day in years that are divisible by 100 but not divisible by 400. Example 1700, 1800, 1900 and 2100 are not leap years.
Actually all 12 mounts have 28 days. Yes it is true that February is the only month that has only 28 days, but they all have at least 28. In December there are 31 days. There are still 28 days in the month.