The important latitudes are the Equator ,the Tropic of Cancer,the Arctic Circle in the north and the Tropic of Capricorn, the Antarctic Circle in the south.
Latitudes help us divide the whole Earth into climatic zones with reference to Equator and are most important while studying the geography of any country.
The important latitudes from North to South are:

Arctic Circle : 66.5° N
Tropic Of Cancer : 23.5° N
Equator : 0°
Tropic of Capricorn : 23.5° S
Antarctic Circle: 66.5° S

These latitudes are of great help while deciding the effect of Sun's heat in different regions.

Location of different places can be specified using latitudes (and longitudes)

Different Zones like Torrid Zone, Temperate Zone and Frigid Zone are specified using the above mentioned latitudes.