It is just like day time-saving in Europe and elsewhere in winter. The solar month is 30–31 days and 365 days a year while

A lunar month from new Moon to new Moon(The Lunar Cycle or Phase ) is 29.5 days which adds only to 354 days (29.5 X12) short of 11 days according to the Solar calendar. Hence in a matter of just 3 solar years, there will be one lunar month difference in pattern as it gets drifted from the normal seasons with the wrong observance.

354 days X 3 Lunar years =1062 days

365X3 Solar years =1095 days

The significance is specially related to farming in ancient times by Egyptians and Chinese so they started to add a Leap month every 3 years to compensate the problem and to avoid drift from solar calendar and seasons to which the celebrations and festivities are coordinated. By doing 11 times the cycle is complete as 33 Solar years get completed and 33 years is the time which by default gets the sync up the Lunar and Solar cycle calendars.

11X3 =33

i.e 33-year cycle.