Farmers need accurate weather predictions; and they rely on calendrical information such as rainfall records from years past— to plan sowing seasons.
2. Religious ceremonies
Calendars allow members of a community to coordinate and schedule important dates like festivals and offerings of religious rituals (i.e.: New Year)
3. Astronomical research/calculations
To study planets, lunar, and solar phenomena which the Maya had detailed and precise knowledge; used to make the 4 calendars. To determine best day to hunt/fish